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Sample records for bouguer gravity anomalies

  1. Complete Bouguer gravity anomaly map of the state of Colorado

    USGS Publications Warehouse

    Abrams, Gerda A.

    1993-01-01

    The Bouguer gravity anomaly map is part of a folio of maps of Colorado cosponsored by the National Mineral Resources Assessment Program (NAMRAP) and the National Geologic Mapping Program (COGEOMAP) and was produced to assist in studies of the mineral resource potential and tectonic setting of the State. Previous compilations of about 12,000 gravity stations by Behrendt and Bajwa (1974a,b) are updated by this map. The data was reduced at a 2.67 g/cm3 and the grid contoured at 3 mGal intervals. This map will aid in the mineral resource assessment by indicating buried intrusive complexes, volcanic fields, major faults and shear zones, and sedimentary basins; helping to identify concealed geologic units; and identifying localities that might be hydrothermically altered or mineralized.

  2. Optimization schemes for the inversion of Bouguer gravity anomalies

    NASA Astrophysics Data System (ADS)

    Zamora, Azucena

    associated with structural changes [16]; therefore, it complements those geophysical methods with the same depth resolution that sample a different physical property (e.g. electromagnetic surveys sampling electric conductivity) or even those with different depth resolution sampling an alternative physical property (e.g. large scale seismic reflection surveys imaging the crust and top upper mantle using seismic velocity fields). In order to improve the resolution of Bouguer gravity anomalies, and reduce their ambiguity and uncertainty for the modeling of the shallow crust, we propose the implementation of primal-dual interior point methods for the optimization of density structure models through the introduction of physical constraints for transitional areas obtained from previously acquired geophysical data sets. This dissertation presents in Chapter 2 an initial forward model implementation for the calculation of Bouguer gravity anomalies in the Porphyry Copper-Molybdenum (Cu-Mo) Copper Flat Mine region located in Sierra County, New Mexico. In Chapter 3, we present a constrained optimization framework (using interior-point methods) for the inversion of 2-D models of Earth structures delineating density contrasts of anomalous bodies in uniform regions and/or boundaries between layers in layered environments. We implement the proposed algorithm using three different synthetic gravitational data sets with varying complexity. Specifically, we improve the 2-dimensional density structure models by getting rid of unacceptable solutions (geologically unfeasible models or those not satisfying the required constraints) given the reduction of the solution space. Chapter 4 shows the results from the implementation of our algorithm for the inversion of gravitational data obtained from the area surrounding the Porphyry Cu-Mo Cooper Flat Mine in Sierra County, NM. Information obtained from previous induced polarization surveys and core samples served as physical constraints for the

  3. World Gravity Map: a set of global complete spherical Bouguer and isostatic anomaly maps and grids

    NASA Astrophysics Data System (ADS)

    Bonvalot, S.; Balmino, G.; Briais, A.; Kuhn, M.; Peyrefitte, A.; Vales, N.; Biancale, R.; Gabalda, G.; Reinquin, F.

    2012-04-01

    We present here a set of digital maps of the Earth's gravity anomalies (surface free air, Bouguer and isostatic), computed at Bureau Gravimetric International (BGI) as a contribution to the Global Geodetic Observing Systems (GGOS) and to the global geophysical maps published by the Commission for the Geological Map of the World (CGMW) with support of UNESCO and other institutions. The Bouguer anomaly concept is extensively used in geophysical interpretation to investigate the density distributions in the Earth's interior. Complete Bouguer anomalies (including terrain effects) are usually computed at regional scales by integrating the gravity attraction of topography elements over and beyond a given area (under planar or spherical approximations). Here, we developed and applied a worldwide spherical approach aimed to provide a set of homogeneous and high resolution gravity anomaly maps and grids computed at the Earth's surface, taking into account a realistic Earth model and reconciling geophysical and geodetic definitions of gravity anomalies. This first version (1.0) has been computed by spherical harmonics analysis / synthesis of the Earth's topography-bathymetry up to degree 10800. The detailed theory of the spherical harmonics approach is given in Balmino et al., (Journal of Geodesy, 2011). The Bouguer and terrain corrections have thus been computed in spherical geometry at 1'x1' resolution using the ETOPO1 topography/bathymetry, ice surface and bedrock models from the NOAA (National Oceanic and Atmospheric Administration) and taking into account precise characteristics (boundaries and densities) of major lakes, inner seas, polar caps and of land areas below sea level. Isostatic corrections have been computed according to the Airy-Heiskanen model in spherical geometry for a constant depth of compensation of 30km. The gravity information given here is provided by the Earth Geopotential Model (EGM2008), developed at degree 2160 by the National Geospatial

  4. A simple Bouguer gravity anomaly map of southwestern Saudi Arabia and an initial interpretation

    USGS Publications Warehouse

    Gettings, M.E.

    1983-01-01

    Approximately 2,200 gravity stations on a 10-km2 grid were used to construct a simple Bouguer gravity anomaly map at 1:2,000,000 scale along a 150-km-wide by 850-km-long strip of the Arabian Peninsula from Sanam, southwest of Ar Riyad, through the Farasan Islands and including offshore islands, the coastal plain, and the Hijaz-Asir escarpment from Jiddah to the Yemen border. On the Precambrian Arabian Shield, local positive gravity anomalies are associated with greenstone belts, gneiss domes, and the Najd fault zones. Local negative gravity anomalies correlate with granitic plutonic rocks. A steep gravity gradient of as much as 4 mgal-km-1 marks the continental margin on the coastal plain near the southwestern end of the strip. Bouguer gravity anomaly values range from -10 to +40 mgal southwest of this gradient and from -170 to -100 mgal in a 300-km-wide gravity minimum northeast of the gradient. Farther northeast, the minimum is terminated by a regional gradient of about 0.1 mgal-km-1 that increases toward the Arabian Gulf. The regional gravity anomaly pattern has been modeled by using seismic refraction and Raleigh wave studies, heat-flow measurements, and isostatic considerations as constraints. The model is consistent with the hypothesis of upwelling of hot mantle material beneath the Red Sea and lateral mantle flow beneath the Arabian plate. The model yields best-fitting average crustal densities of 2.80 g-cm-3 (0-20 km depth) and 3.00 g-cm-3 (20-40 km depth) southwest of the Nabitah suture zone and 2.74 g-cm-3 (0-20 km depth) and 2.94 g-cm-3 (20-40 km depth) northeast of the suture zone. The gravity model requires that the crust be about 20 km thick at the continental margin and that the lower crust between the margin and Bishah (lat 20? N., long 42.5? E.) be somewhat denser than the lower crust to the northeast. Detailed correlations between 1:250,000- and 1:500,000-scale geologic maps and the gravity anomaly map suggest that the greenstone belts associated

  5. Principal facts and a discussion of terrain correction methods for the complete Bouguer gravity anomaly map of the Cascade Mountains, Washington

    SciTech Connect

    Danes, Z.F.; Phillips, W.M.

    1983-02-01

    Since 1974, the Division of Geology and Earth Resources, in conjunction with the US Department of Energy, has supported gravity studies in the Cascade Mountains of Washington State. Results of the Cascade gravity project are summarized graphically as a complete Bouguer gravity anomaly map of the Cascade Mountains, Washington (Danes and Phillips, 1983). This report provides supplementary data and documentation for the complete Bouguer gravity anomaly map. Presented are principal gravity facts, simple Bouguer and Free-air gravity anomalies, computational methods, error analysis and a discussion of terrain corrections.

  6. Bouguer gravity anomaly and isostatic residual gravity maps of the Tonopah 1 degree by 2 degrees Quadrangle, central Nevada

    USGS Publications Warehouse

    Plouff, Donald

    1992-01-01

    A residual isostatic gravity map (sheet 2) was prepared so that the regional effect of isostatic compensation present on the Bouguer gravity anomaly map (sheet 1) would be minimized. Isostatic corrections based on the Airy-Heiskanen system (Heiskanen and Vening Meinesz, 1958, p. 135-137) were estimated by using 3-minute topographic digitization and applying the method of Jachens and Roberts (1981). Parameters selected for the isostatic model were 25 km for the normal crustal thickness at sea level, 2.67 g/cm3 for the density of the crust, and 0.4 g/cm3 for the contrast in density between the crust and the upper mantle. These parameters were selected so that the isostatic residual gravity map would be consistent with isostatic residual gravity maps of the adjacent Walker Lake quadrangle (Plouff, 1987) and the state of Nevada (Saltus, 1988c).

  7. Data reduction and tying in regional gravity surveys—results from a new gravity base station network and the Bouguer gravity anomaly map for northeastern Mexico

    NASA Astrophysics Data System (ADS)

    Hurtado-Cardador, Manuel; Urrutia-Fucugauchi, Jaime

    2006-12-01

    Since 1947 Petroleos Mexicanos (Pemex) has conducted oil exploration projects using potential field methods. Geophysical exploration companies under contracts with Pemex carried out gravity anomaly surveys that were referred to different floating data. Each survey comprises observations of gravity stations along highways, roads and trails at intervals of about 500 m. At present, 265 separate gravimeter surveys that cover 60% of the Mexican territory (mainly in the oil producing regions of Mexico) are available. This gravity database represents the largest, highest spatial resolution information, and consequently has been used in the geophysical data compilations for the Mexico and North America gravity anomaly maps. Regional integration of gravimeter surveys generates gradients and spurious anomalies in the Bouguer anomaly maps at the boundaries of the connected surveys due to the different gravity base stations utilized. The main objective of this study is to refer all gravimeter surveys from Pemex to a single new first-order gravity base station network, in order to eliminate problems of gradients and spurious anomalies. A second objective is to establish a network of permanent gravity base stations (BGP), referred to a single base from the World Gravity System. Four regional loops of BGP covering eight States of Mexico were established to support the tie of local gravity base stations from each of the gravimeter surveys located in the vicinity of these loops. The third objective is to add the gravity constants, measured and calculated, for each of the 265 gravimeter surveys to their corresponding files in the Pemex and Instituto Mexicano del Petroleo database. The gravity base used as the common datum is the station SILAG 9135-49 (Latin American System of Gravity) located in the National Observatory of Tacubaya in Mexico City. We present the results of the installation of a new gravity base network in northeastern Mexico, reference of the 43 gravimeter surveys

  8. Principal Facts and a Discussion of Terrain Correction Methods for the Complete Bouguer Gravity Anomaly Map of the Cascade Mountains, Washington

    SciTech Connect

    Danes, Z.F.; Phillips, William M.

    1983-02-01

    Since 1974, the Division of Geology and Earth Resources, in conjunction with the US Department of Energy, has supported gravity studies in the Cascade Mountains of Washington State (Danes, 1975, 1979, 1981; Korosec and others, 1981). The purpose of the work has been to gather baseline gravity data for eventual contribution to geothermal resource evaluation. However, it is expected that the Cascade gravity data will prove useful in a number of future endeavors such as fossil fuel and mineral exploration, as the gravity method is a basic tool of the exploration geophysicist. Results of the Cascade gravity project are summarized graphically as a complete Bouguer gravity anomaly map of the Cascade Mountains, Washington. This report provides supplementary data and documentation for the complete Bouguer gravity anomaly map. Presented are principal gravity facts, simple Bouguer and Free-air gravity anomalies, computational methods, error analysis and a discussion of terrain corrections. It is hoped that release of this report will encourage analysis of Cascade gravity data beyond the standard treatment (complete Bouguer gravity anomaly at a reduction density of 2.67 g/cm{sup 2}) presented in Danes and Phillips, (1983).

  9. A new Bouguer gravity anomaly field for the Adriatic Sea and its application for the study of the crustal and upper mantle structure

    NASA Astrophysics Data System (ADS)

    Tassis, G. A.; Grigoriadis, V. N.; Tziavos, I. N.; Tsokas, G. N.; Papazachos, C. B.; Vasiljević, I.

    2013-05-01

    The purpose of this paper is the development of a new Bouguer anomaly map for the broader Adriatic Sea area to be used as geo-scientific tool which will answer questions mainly regarding the deep and intermediate depth structure of the Adriatic and its surrounding areas. As a first step, a consistent, high-resolution and accuracy free-air gravity anomaly database is created using all the available terrestrial and satellite altimetry data sources. The least-squares collocation (LSC) method is employed to validate the different gravity data sets through an appropriate covariance analysis and following the remove-compute-restore procedure (RCR) for the detailed study of the gravity spectrum. The finally generated gravity database has a resolution of a 0.0333° (˜3.2 km) in both latitude and longitude, while its external and internal accuracy is estimated to about ±5 mGal and ±0.5 mGal, respectively. Based on the derived free-air gravity database a new Bouguer gravity anomaly database is determined at the same resolution for the wider region of the Adriatic Sea. Comparison with existing results confirms the reliability of the new Bouguer map for the study area, mainly due to the combination of both land and sea data. The derived Bouguer anomaly map can support different kind of geophysical investigations of both local and regional structure of the study region. As an example three density models are constructed along selected cross sections extracted from the Bouguer anomaly database, in order to obtain structural information for the crustal-upper mantle structure of the region and draw relevant conclusions. The obtained results show that the Bouguer map can provide important information for the lower-crustal/upper-mantle depth range but also helps to constrain the 2D geometry of the shallow geological units, in very good agreement with the observed surface geology and the current understanding of the geotectonic setting of the area.

  10. GTeC-A versatile MATLAB® tool for a detailed computation of the terrain correction and Bouguer gravity anomalies

    NASA Astrophysics Data System (ADS)

    Cella, Federico

    2015-11-01

    Gravity Terrain Correction (GTeC) is a versatile MATLAB® code for terrain correction aimed to this purpose and capable of going beyond the limits of other public domain codes targeted to this aim. It runs with input gravity data (absolute measurements or free air anomalies) at the land/sea surface and with one or more DTMs (indifferently gridded or scattered) at different detail levels. Each of them can be used to calculate the gravity contribution of a concentric terrain zone around the point station with increasing resolution toward the center. The user can choose between two alternative algorithms for terrain modeling. The simplest one considers each grid point as the flat top of a squared prism. For areas closer to the point station a second algorithm can be chosen to better approximate the relief, with respect to others formulas, by means of a tessellation based network formed by triangular prisms. A more precise terrain correction is therefore achieved, especially in presence of high topographic gradients or just outside the sea/land boundaries. In the last case a suitable algorithm was expressly devised to fit the tessellation based network to the irregular trend of the coastline. GTeC calculates also free air anomalies and both plate and curvature corrections, providing also a complete graphic output including topography, free air anomalies, plate correction, total terrain correction, Bouguer anomalies and the terrain effect due to each computational zone. GTeC speeds up CPU times taking advantage from the parallel computing functions and from the vectorization code, both exploited in MATLAB®. Two code versions of GTeC (for normal or parallel computation), executable under MATLAB environment (pcode), are fully available as public domain software. The results of a synthetic case, of a real case at the regional scale and of a microgravity survey carried out at a short scale, are here presented.

  11. Bouguer gravity anomaly map of the Twentynine Palms Marine Corps Base and vicinity, California

    USGS Publications Warehouse

    Moyle, W.R., Jr.

    1984-01-01

    A gravity study of the Twentynine Palms Marine Corps Base and vicinity, California, based on 495 gravity measurements, has been completed. The resulting contour map of the area shows that the ground-water basin ranges in depth from less than a foot at the edges of the basin to about 10,500 feet at the center of a gravity low near Deadman Lake. This study will aid in later studies to determine quantities of water in storage beneath the Marine Corps Base. (USGS)

  12. On the Optimization of the Inverse Problem for Bouguer Gravity Anomalies

    NASA Astrophysics Data System (ADS)

    Zamora, A.; Velasco, A. A.; Gutierrez, A. E.

    2013-12-01

    Inverse modeling of gravity data presents a very ill-posed mathematical problem, given that solutions are non-unique and small changes in parameters (position and density contrast of an anomalous body) can highly impact the resulting Earth's model. Although implementing 2- and 3-Dimensional gravitational inverse problems can determine the structural composition of the Earth, traditional inverse modeling approaches can be very unstable. A model of the shallow substructure is based on the density contrasts of anomalous bodies -with different densities with respect to a uniform region- or the boundaries between layers in a layered environment. We implement an interior-point method constrained optimization technique to improve the 2-D model of the Earth's structure through the use of known density constraints for transitional areas obtained from previous geological observations (e.g. core samples, seismic surveys, etc.). The proposed technique is applied to both synthetic data and gravitational data previously obtained from the Rio Grande Rift and the Cooper Flat Mine region located in Sierra County, New Mexico. We find improvements on the models obtained from this optimization scheme given that getting rid of geologically unacceptable models that would otherwise meet the required geophysical properties reduces the solution space.

  13. Worldwide complete spherical Bouguer and isostatic anomaly maps

    NASA Astrophysics Data System (ADS)

    Bonvalot, S.; Balmino, G.; Briais, A.; Peyrefitte, A.; Vales, N.; Biancale, R.; Gabalda, G.; Reinquin, F.

    2011-12-01

    We present here a set of digital maps of the Earth's gravity anomalies (surface "free air", Bouguer and isostatic), computed at Bureau Gravimetric International (BGI) as a contribution to the Global Geodetic Observing Systems (GGOS) and to the global geophysical maps published by the Commission for the Geological Map of the World (CGMW). The free air and Bouguer anomaly concept is extensively used in geophysical interpretation to investigate the density distributions in the Earth's interior. Complete Bouguer anomalies (including terrain effects) are usually computed at regional scales by integrating the gravity attraction of topography elements over and beyond a given area (under planar or spherical approximations). Here, we developed and applied a worldwide spherical approach aimed to provide a set of homogeneous and high resolution gravity anomaly maps and grids computed at the Earth's surface, taking into account a realistic Earth model and reconciling geophysical and geodetic definitions of gravity anomalies. This first version (1.0) has been computed by spherical harmonics analysis / synthesis of the Earth's topography-bathymetry up to degree 10800. The detailed theory of the spherical harmonics approach is given in Balmino et al., (Journal of Geodesy, submitted). The Bouguer and terrain corrections have thus been computed in spherical geometry at 1'x1' resolution using the ETOPO1 topography/bathymetry, ice surface and bedrock models from the NOAA (National Oceanic and Atmospheric Administration) and taking into account precise characteristics (boundaries and densities) of major lakes, inner seas, polar caps and of land areas below sea level. Isostatic corrections have been computed according to the Airy Heiskanen model in spherical geometry for a constant depth of compensation of 30km. The gravity information given here is provided by the Earth Geopotential Model (EGM2008), developed at degree 2160 by the National Geospatial Intelligence Agency (NGA) (Pavlis

  14. Aeromagnetic and complete Bouguer gravity anomaly maps of the Hunter-Fryingpan Wilderness area, Pitkin County, Colorado

    USGS Publications Warehouse

    Campbell, D.L.

    1981-01-01

    Behrendt and others (1968) pointed out the close correlation between a belt of extreme gravity lows (Behrendt and Bajwa, 1974) and a zone of precious and base mineral deposits (Tweto and Simms, 1963, fig. 1).  Tweto and Case (1972) showed that this belt of gravity lows probably reflects a series of Laramide and post-Laramide intrusions of relatively low density which may have influenced the hydrothermal systems responsible for much of the mineralization in the Colorado Mineral Belt.

  15. Bouguer Anomaly of the Solfatara Hydrothermal Plume, Campi Flegrei

    NASA Astrophysics Data System (ADS)

    Young, N. K.; Gottsmann, J.

    2015-12-01

    Solfatara tuff cone is the most hydrothermally active area within Campi Flegrei caldera, a resurgent nested caldera near Naples, Italy. Hydrothermal gases and fluids are released most vigorously here and at Pisciarelli nearby. Models explaining the measured fumarole emissions and deformation require a plume of ascending hot water vapour and CO2 from depth. Here we present preliminary findings from a new gravity survey which aims at i) creating a high precision Bouguer anomaly map of Solfatara and ii) imaging the hydrothermal plume. We carried out a high spatial density gravity survey of Solfatara and the surrounding area using a Scintrex CG5 gravimeter and simultaneous benchmark localisation using a GNSS system. We created a dense grid of 51 stations within Solfatara crater, and a reduced density network of 37 further stations outside the crater to 3km distance. Other geophysical techniques such as electromagnetism, electrical resistivity, and active seismic imaging have resolved the subsurface architecture to depths between a few hundred meters to 3km depth. Our coverage and spacing should capture the details of the plume under Solfatara and have resolution to approximately 3km depth.

  16. Local gravity anomalies produced by dislocation sources.

    USGS Publications Warehouse

    Savage, J.C.

    1984-01-01

    Dilatancy, in general, does not correspond to the absence of a free air anomaly, as might be suggested by the special case of a spherical source of dilatation. For two-dimensional models a cylindrical source of dilatation produces no free air gravity anomaly, dip-slip faulting produces no Bouguer anomaly, and open cracks produce a Bouguer anomaly equal to that which would be produced had the material within the crack been mined out without deforming the solid. -from Author

  17. An updated Bouguer anomaly map of south-central West Africa

    USGS Publications Warehouse

    Hastings, David A.

    1983-01-01

    A new Bouguer gravity anomaly map compiled for western Africa adds data for Ghana, Guinea, and Liberia.The new data add detail to a key part of the Eburnean shield and assist in the development of a model of rifting at the time of the Eburnean orogeny, 2000 million years ago. This model includes a framework for the deposition of the region's mineral deposits. The model and existing field data can be used to guide future minerals exploration in the region.

  18. New free-air and Bouguer gravity fields of Taiwan from multiple platforms and sensors

    NASA Astrophysics Data System (ADS)

    Hwang, Cheinway; Hsu, Hung-Jui; Chang, Emmy T. Y.; Featherstone, W. E.; Tenzer, Robert; Lien, Tzuyi; Hsiao, Yu-Shen; Shih, Hsuan-Chang; Jai, Pang-Ho

    2014-01-01

    We construct 1‧ × 1‧ grids of free-air and Bouguer gravity anomalies around Taiwan with well-defined error estimates for quality assessment. The grids are compiled from land, airborne and shipborne gravity measurements, augmented with altimeter gravity at sea. Three sets of relative land gravity measurements are network-adjusted and outlier-edited, yielding accuracies of 0.03-0.09 mGal. Three airborne gravity sets are collected at altitudes 5156 and 1620 m with accuracies of 2.57-2.79 mGal. Seven offshore shipborne gravity campaigns around Taiwan and its offshore islands yield shallow-water gravity values with 0.88-2.35 mGal accuracies. All data points are registered with GPS-derived geodetic coordinates at cm-dm accuracies, allowing for precise gravity reductions and computing gravity disturbances. The various datasets are combined by the band-limited least-squares collocation in a one-step procedure. In the eastern mountainous (or offshore) region, Bouguer anomalies and density contrasts without considering the oceanic (or land) topographic contribution are underestimated. The new grids show unprecedented tectonic features that can revise earlier results, and can be used in a broad range of applications.

  19. Seismic b-Values, Bouguer Gravity and Heat Flow Data Beneath Eastern Anatolia, Turkey: Tectonic Implications

    NASA Astrophysics Data System (ADS)

    Maden, Nafiz; Öztürk, Serkan

    2015-07-01

    In this paper, we analyze the relationships between the seismic b-values, Bouguer gravity and heat flow data in the Eastern Anatolia region of Turkey. For this purpose, spatial distributions of b-value, Bouguer gravity and heat flow have been presented for different depths and locations. In distinction to previous studies which have used only two parameters (gravity and seismic b-value or heat flow and seismic b-value), we have combined seismic b-values, Bouguer gravity and heat flow data to determine the new results on the active tectonics of the Eastern Anatolia region. Our analysis shows that there are significant and robust correlations amidst the heat flow data, Bouguer gravity anomaly and seismic b-values. The crustal structure is thick in areas where the large negative gravity anomalies and low b-values are observed. On the contrary, the regions with positive gravity anomalies and high b-values are likely to be associated with magma chambers or crustal low-velocity zones. We also provide some evidence suggesting that high b-values and high heat flow values can be related to the magmatic activities beneath the volcanic chain in the Eastern Pontide orogenic belt. Consequently, we have reached some conclusions for the Eastern Anatolia region: (1) The Moho to surface is rather thick and earthquakes are relatively smaller beneath the volcanic chain where the high heat flow values are observed, (2) a southward subduction model could have existed for the development of the Pontides during the late Mesozoic-Cenozoic era, (3) hot and unstable mantle lid zones or a lithosphere deprived of mantle under the study region is much more plausible, (4) a southward movement of the subduction plate and a northward extension of the Black Sea increase the state of stress along the trench axis and decrease the b-value, and (5) these movements may load the stress energy to the fault zones, thereby causing the catastrophic earthquakes in the Eastern Anatolia region.

  20. Fractal Characteristics of Geomorphology Units as Bouguer Anomaly Manifestations in Bumiayu, Central Java, Indonesia

    NASA Astrophysics Data System (ADS)

    Agus Nur, Andi; Syafri, Ildrem; Muslim, Dicky; Hirnawan, Febri; Raditya, Pradnya P.; Sulastri, Murni; Abdulah, Fikri

    2016-01-01

    Bumiayu in Central Java, Indonesia, has a typical landform characteristics. Differences of topography on each geomorphological unit indicated by the value of fractal dimension. This research provides important information on the influence of geomorphology conditions and subsurface geological phenomenon of research area based on fractal application. This research methodology relies on laboratory analysis and field observation. Landform is a characteristics of Bouguer anomaly contour manifestation. It is indicated by occurences of significant correlation between the Bouguer anomaly countour and geological cross section as well topography contour slope and Bouguer anomaly contour slope. Based on spatial analysis, morphology of research area is dominated by very high steep hills (more than 60%). Result of Bouguer anomaly countour analysis also shows that research area dominated by very high steep hills (more than 55%). Statistical analysis between the fractal value of lineament in Digital Elevation Model and fractal value of lineament in Bouguer anomaly countour as well the fractal value of topography countour and fractal value of Bouguer anomaly countour shows that the relationship was not significant. Further, the entire result of this verified research shows clearly that geomorphology conditions represents subsurface geological phenomenon.

  1. On Gravity Inversion by No-Topography and Rigorous Isostatic Gravity Anomalies

    NASA Astrophysics Data System (ADS)

    Sjöberg, Lars E.; Bagherbandi, Mohammad; Tenzer, Robert

    2015-10-01

    We discuss some theoretical aspects and practical consequences of using traditional versus "new"/rigorous formulations of the Bouguer and isostatic gravity anomalies/disturbances. In principle, the differences between these two concepts are in the definition of the so-called secondary indirect topographic effect (SITE) on the gravity data. Although we follow the tradition to call this effect SITE, we show that it is formally a direct topographic effect (DITE), needed to remove all topographic signal, but in practice not regarded as such. Consequently, there is a need for a no- topography gravity anomaly, which removes all topographic effects, leaving the below-crust Earth transparent for gravity inversion. Similarly, a rigorous isostatic gravity anomaly includes also a compensation effect for the SITE. By using a simple topographic model, we confirm a theoretically found ratio of 2/( n + 1) between the magnitudes of the SITE and DITE by wavelength (spherical harmonic degree n), both for the Bouguer and isostatic gravity anomalies. Finally, global gravity inversions are applied by utilizing the Vening Meinesz-Moritz isostatic model to determine the Moho geometry using the Bouguer gravity disturbances/anomalies and the no-topography gravity anomalies, and the results are compared. The numerical results confirm our theoretical findings that the Bouguer gravity disturbances and the no-topography gravity anomalies provide very similar results. A comparison of these gravimetrically computed Moho depths with the CRUST1.0 seismic model shows rms agreements of 4.3 and 4.5 km, respectively. This is a significant improvement when compared to the Moho result obtained by using the Bouguer gravity anomalies, yielding the rms difference of 7.3 km for the CRUST1.0 model. These results confirm a theoretical deficiency of the classical definition of the Bouguer and isostatic gravity anomalies, which do not take into consideration the SITE effects on the topography and its

  2. Eastern US crustal thickness estimates from spectral analysis and inversion of onshore Bouguer gravity anaomalies

    NASA Astrophysics Data System (ADS)

    Dybus, W.; Benoit, M. H.; Ebinger, C. J.

    2011-12-01

    The crustal thickness beneath much of the eastern half of the US is largely unconstrained. Though there have been several controlled source seismic surveys of the region, many of these studies suffer from rays that turn in the crust above the Moho, resulting in somewhat ambiguous crustal thickness values. Furthermore, the broadband seismic station coverage east of the Mississippi has been limited, and most of the region remains largely understudied. In this study, we estimated the depth to the Moho using both spectral analysis and inversion of Bouguer gravity anomalies. We systematically estimated depths to lithospheric density contrasts from radial power spectra of Bouguer gravity within 100 km X 100 km windows eastward from the Mississippi River to the Atlantic Coast, and northward from North Carolina to Maine. The slopes and slope breaks in the radial power spectra were computed using an automated algorithm. The slope values for each window were visually inspected and then used to estimate the depth to the Moho and other lithospheric density contrasts beneath each windowed region. Additionally, we performed a standard Oldenburg-Parker inversion for lithospheric density contrasts using various reference depths and density contrasts that are realistic for the different physiographic provinces in the Eastern US. Our preliminary results suggest that the gravity-derived Moho depths are similar to those found using seismic data, and that the crust is relatively thinner (~28-33 km) than expected in beneath the Piedmont region (~35-40 km). Given the relative paucity of seismic data in the eastern US, analysis of onshore gravity data is a valuable tool for interpolating between seismic stations.

  3. Imaging subsurface density distribution beneath Montserrat (West Indies) from Bouguer gravity data

    NASA Astrophysics Data System (ADS)

    Hautmann, S.; Camacho, A. G.; Gottsmann, J.; Odbert, H. M.; Syers, T.

    2012-12-01

    High resolution static gravity data allow to resolve for spatial inhomogeneities in the Earth's gravity field by providing information on the density distribution in the shallow subsurface. Images of the subsurface density distribution and identification of structural discontinuities in the ground are of particular interest in active volcanic regions, as they bear implications for fluid migration, edifice stability and the subsurface transmission of volcanically induced stresses. Although the persistently active Soufrière Hills Volcano (SHV; Montserrat, West Indies) is currently one of the most extensively studied actively erupting stratovolcanos, a local Bouguer anomaly map of the volcano and the island of Montserrat is missing to date. In June/July 2012 we conducted a static gravity survey on Montserrat. Using a Scintrex CG-5 Autograv a total of 160 new gravity data were collected on the entire island. Site positions and elevations were obtained via a TOPCON Hiperpro dual frequency GNSS receiver/antenna. Our Bouguer gravity network provides a dense coverage (distance of 200 m between adjacent sites) of the accessible regions of the older volcanic complexes Silver Hills and Centre Hills, while (due to operator's safety) the network coverage around the active SHV is more sparse with about 1 km distance between adjacent sites. The recorded gravity data were corrected for Solid Earth Tides and ocean loading and reduced for the effect of benchmark elevation (free-air effect) and latitude. The correction for topographic effects was done via an automated algorithm based on a digital elevation model and bathymetric data. In order to model our data we performed a non-linear inversion using the inversion package GROWTH 2.0. The inversion is based on a 3-D aggregation of M parallelepiped cells, which are filled, in a growth process, by means of prescribed positive and/or negative density contrasts. This methodology provides, via an automatic approach, a free 3-D geometry

  4. Band-limited Bouguer gravity identifies new basins on the Moon

    NASA Astrophysics Data System (ADS)

    Featherstone, W. E.; Hirt, C.; Kuhn, M.

    2013-06-01

    Spectral domain forward modeling is used to generate topography-implied gravity for the Moon using data from the Lunar Orbiter Laser Altimeter instrument operated on board the Lunar Reconnaissance Orbiter mission. This is subtracted from Selenological and Engineering Explorer (SELENE)-derived gravity to generate band-limited Bouguer gravity maps of the Moon so as to enhance the gravitational signatures of anomalous mass densities nearer the surface. This procedure adds evidence that two previously postulated basins on the lunar farside, Fitzgerald-Jackson (25°N, 191°E) and to the east of Debye (50°N, 180°E), are indeed real. When applied over the entire lunar surface, band-limited Bouguer gravity reveals the locations of 280 candidate basins that have not been identified when using full-spectrum gravity or topography alone, showing the approach to be of utility. Of the 280 basins, 66 are classified as distinct from their band-limited Bouguer gravity and topographic signatures, making them worthy of further investigation.

  5. Gravity anomaly and crustal density structure in Jilantai rift zone and its adjacent region

    NASA Astrophysics Data System (ADS)

    Wu, Guiju; Shen, Chongyang; Tan, Hongbo; Yang, Guangliang

    2016-08-01

    This paper deals with the interpretation of Bouguer gravity anomalies measured along a 250 km long Suhaitu-Etuokeqi gravity profile located at the transitional zone of the Alxa and Ordos blocks where geophysical characteristics are very complex. The analysis is carried out in terms of the ratio of elevation and Bouguer gravity anomaly, the normalized full gradient of a section of the Bouguer gravity anomaly (G h ) and the crustal density structure reveal that (1) the ratio of highs and lows of elevation and Bouguer gravity anomaly is large between Zhengyiguan fault (F4) and Helandonglu fault (F6), which can be explained due to crustal inhomogeneities related to the uplift of the Qinghai-Tibet block in the northeast; (2) the main active faults correspond to the G h contour strip or cut the local region, and generally show strong deformation characteristics, for example the Bayanwulashan mountain front fault (F1) or the southeast boundary of Alxa block is in accord with the western change belt of G h , a belt about 10 km wide that extends to about 30 km; (3) Yinchuan-Pingluo fault (F8) is the seismogenic structure of the Pingluo M earthquake, and its focal depth is about 15 km; (4) the Moho depth trend and Bouguer gravity anomaly variation indicates that the regional gravity field is strongly correlated with the Moho discontinuity.

  6. Bouguer gravity trends and crustal structure of the Palmyride Mountain belt and surrounding northern Arabian platform in Syria

    SciTech Connect

    Best, J.A.; Barazangi, M. ); Al-Saad, D.; Sawaf, T.; Gebran, A. )

    1990-12-01

    This study examines the crustal structure of the Palmyrides and the northern Arabian platform in Syria by two- and three-dimensional modeling of the Bouguer gravity anomalies. Results of the gravity modeling indicate that (1) western Syria is composed of at least two different crustal blocks, (2) the southern crustal block is penetrated by a series of crustal-scale, high-density intrusive complexes, and (3) short-wavelength gravity anomalies in the southwest part of the mountain belt are clearly related to basement structure. The crustal thickness in Syria, as modeled on the gravity profiles, is approximately 40{plus minus}4 km, which is similar to crustal thicknesses interpreted from refraction data in Jordan and Saudi Arabia. The different crustal blocks and large-scale mafic intrusions are best explained, though not uniquely, by Proterozoic convergence and suturing and early Paleozoic rifting, as interpreted in the exposed rocks of the Arabian shield. These two processes, combined with documented Mesozoic rifting and Cenozoic transpression, compose the crustal evolution of the northern Arabian platform beneath Syria.

  7. Detection of Lineaments in Denizli Basin of Western Anatolia Region Using Bouguer Gravity Data

    NASA Astrophysics Data System (ADS)

    Altinoğlu, Figen F.; Sari, Murat; Aydin, Ali

    2015-02-01

    The aim of this study is to investigate the geostructural boundaries of the eastern part of Western Anatolia. To achieve this, three methods, horizontal gradient, analytic signal, and tilt angle, were used. With the application of each method to the Bouguer gravity data, the common lineaments were determined using maximum values of the horizontal gradient, analytic signal maps, and zero contours of the tilt angle maps. The basement topography was also produced using the Parker-Oldenburg algorithm. Then, the produced lineaments were compared with the active fault map of the region. The results suggested that although a good agreement between the current work and earlier work exists, the new four lineament regions were also detected. We concluded that this work will lead to better understanding of Anatolian geostructural and its impact on the larger scale geological processes.

  8. Study of Southern Tyrrhenian and Sicilian regions by a sequential procedure to integrate WAM seismic tomographies and Bouguer anomaly data

    NASA Astrophysics Data System (ADS)

    Panepinto, S.; Calo, M. M.; Luzio, D.; Dorbath, C.

    2009-12-01

    A procedure to obtain 3D velocity-density models and earthquake relocation by integrated inversion of P and S wave traveltimes and Bouguer anomaly distribution was applied to a large dataset concerning the Southern Tyrrhenian and Sicilian areas. The seismic dataset was subdivided into two subsets for separate inversions, whose results were later on joined by the WAM (Weighted Average Model) technique. This is a post-processing technique proposed by Calò et al. (2009) by which preliminary tomographic models are unified in a common 3D grid. The first dataset concerns 28873 P and 9990 S arrival times of 1800 earthquakes located in the area 14°30‧ E - 17°E, 37°N - 41°N while the second dataset contains 31250 P and 13588 S arrival-times related to 1951 events located in the area 11° E - 15°48‧ E, 36°30‧N - 39°N. The selected events were recorded at least by 10 stations in the period 1981-2005 and marked by RMS < 0.50 s. The second dataset was integrated with P-wave traveltimes picked in several sesmic profiles carried out in the study region. The Bouguer anomaly measurements were interpolated in the nodes of a 8x8 km regular grid covering the area 12° E - 16°01‧ E, 36°13‧ N - 38°31‧ N. The proposed procedure allows to invert seismic and gravimetric data with a sequential technique to avoid the problematic optimization of the relative weights to assign to the different type of data. A first WAM provides a preliminary Vp, Vs and Vp/Vs models and a first ipocentral relocation. Since the obtained Vs model seems poorly constrained by the S wave arrival times, the Vp model is converted in a new Vs model, through a Vs-Vp correlation law proposed by T.M. Brocher (2005), and used, jointly to the Vp model, as input for a second WAM. The results of this second step are used to derive, by the empirical Brocher’s equations, 2 density distributions associated to the Vp and Vs models. These density models are statistically compared and the distribution of

  9. On the isostatic gravity anomaly and disturbance and their applications to Vening Meinesz-Moritz gravimetric inverse problem

    NASA Astrophysics Data System (ADS)

    Sjöberg, Lars E.

    2013-06-01

    In this study, we show that the traditionally defined Bouguer gravity anomaly needs a correction to become `the no-topography gravity anomaly' and that the isostatic gravity anomaly is better defined by the latter anomaly plus a gravity anomaly compensation effect than by the Bouguer gravity anomaly plus a gravitational compensation effect. This is because only the new isostatic gravity anomaly completely removes and compensates for the topographic effect. F. A. Vening Meinesz' inverse problem in isostasy deals with solving for the Moho depth from the known external gravity field and mean Moho depth (known, e.g. from seismic reflection data) by a regional isostatic compensation using a flat Earth approximation. H. Moritz generalized the problem to that of a global compensation with a spherical mean Earth approximation. The problem can be formulated mathematically as that of solving a non-linear Fredholm integral equation. The solutions to these problems are based on the condition of isostatic balance of the isostatic gravity anomaly, and, theoretically, this assumption cannot be met by the old definition of the isostatic gravity anomaly. We show how the Moho geometry can be solved for the gravity anomaly, gravity disturbance and disturbing potential, etc., and, from a theoretical point of view, all these solutions are the same.

  10. Sedimentary cover in the South Western Desert of Egypt as deduced from Bouguer gravity and drill-hole data

    NASA Astrophysics Data System (ADS)

    Senosy, M. M.; Youssef, M. M.; Abdel Zaher, M.

    2013-06-01

    The Western Desert, Egypt includes the major groundwater aquifer in the country. It is apart from the Major Sahara Nubian Aquifer which is present in Sudan, Chad, Egypt and Libya. Thickness of this aquifer is changed laterally from south to north and also from west to east. The changes may structurally or litheologicalley control. The present study is focused on using of Bouguer gravity anomaly mapped at a scale of 1:500,000 and the lithological logs of about 120 deep wells used to determine the thickness of the sedimentary sequence containing the main Nubian sandstone water aquifer in important area of Egypt. The area is located in the southern part of the Western Desert bounded by the latitudes 22°00'-26°30'N, and longitudes 28°30'-33°00'E. The predominant structures affecting the basement rocks and the sedimentary cover were traced and analyzed. The gravity stripping approach was applied to eliminate the gravity effects caused by sedimentary sequence and to separate density anomalies within the sedimentary fill from the influence of rocks at deeper levels in the crystalline crust. The study indicated that the surface of the basement rocks is highly rugged and mostly controlled by structures which have a direct effect on thickness variation of the sedimentary cover all over the area. Regionally the area is characterized by two major intracratonic basins (the Dahkla Basin and the Nile valley Basin) separated by a NE-SW trending swell of the Kharga uplift and bounded at the south by the Oweinat-Bir Safsaf-Aswan uplift. These major tectonic units are controlled by fault structures trending in N-S, E-W, NE-SW, NW-SE, which cut the basement rocks and extend upward in the sedimentary cover. The maximum thickness of sandstone formations is recorded at west Oweinat, west Kurkur, southwest of Aswan, Gramashin, Dakhla oasis and some localities west of Sohag and Qena towns. At these localities the thickness ranges between 600 and 900 m. As this formation is the main

  11. Constraints on the deep structure and dynamic processes beneath the Alps and adjacent regions from an analysis of gravity anomalies

    NASA Technical Reports Server (NTRS)

    Lyon-Caen, Helene; Molnar, Peter

    1989-01-01

    Gravity anomalies over the Alps and the Molasse Basin are examined, focusing on the relationship between the anomalies and the tectonic processes beneath the region. Bouguer gravity anomalies measured in France, Germany, Italy, and Switzerland are analyzed. No large isostatic anomalies are observed over the Alps and an elastic model is unable to account for gravity anomalies over the Molasse Basin. These results suggest that the dynamic processes that flexed the European plate down, forming the Molasse Basin and building the Alpine chain, have waned. It is proposed that the late Cenozoic uplift of the region may be due to a diminution or termination of downwelling of mantle material.

  12. Conversion of Bouguer Gravity Data to Depth, Dip, And Density Contrast With Complex Attributes Analysis Technique in the Area of Greece.

    NASA Astrophysics Data System (ADS)

    Kavaja, V.; Reci, H.; Tsokas, G.

    2005-05-01

    The complex attributes analysis is an operator used in the extracting parameters of the buried structures with susceptibility and density contrasts distributions, which lead to the gravity and magnetic anomalies in the region of interest. In this paper is presented the complex attributes analysis of gravity field filtered for wavelengths lower than 50 km in the territory of Greece. The area o Greece has a complex tectonic history and fault system dominated by the subduction of the African plate beneath the Euroasia. A Low-pass filter is used on the Bouguer Anomaly to cut off wavelengths lower than 50Km in order to delineate the major faults structures of interests at big depths. The complex attributes technique aids in interpretation of potential field anomalies, because it can delineate the edges of concealed targets. In obtaining the source parameters from the complex attributes like the local depth, strike and dip, the assumption of sloping contact for the subsurface model is used. The estimated local parameters are in agreement with results obtained by previous interpretations. They can be used in combination with other method to interpret the anomalous field.

  13. Comparison of onshore Bouguer anomalies with GOCE Satellite Data in two sections of the Andes: at 29°S and at 39°S.

    NASA Astrophysics Data System (ADS)

    Alvarez, O.; Gimenez, M.; Braitenberg, C.; Martinez, P.

    2012-04-01

    In the present work we compare the Bouguer anomaly obtained from onshore measurements with the Bouguer anomaly obtained from satellite GOCE data along two well known sections of the Andes, at 29°18'S and at 38°45'S. The first gravimetric section, published by Martinez et al. (2006), describes a gravity and altimetric profile that extends over a distance surpassing 800km in Argentina, at 29°18'S. Using gravimetric inversion methods a crustal model was obtained which is in accordance with the main regional geologic structures. This model fits with a dominant collision mechanism that affected ancient blocks and is a two-layer crustal model with lateral density variations. The Chilenia, Cuyania, Famatina System, Pampia and River Plate cratons were detected. From the gravimetric signal we identify beyond doubt the suture zone between the Precordillera and the Famatina System Ranges, as well as the shear zone between the latter ranges and the Velasco Range. The maximum crustal thickness determined beneath the Andean Cordillera at this latitude is 69 km, whereas under the Famatina System and the Velasco Ranges the values obtained are, respectively, 56 km and 46.5 km. The second profile was published by Folguera et al., (2008). The western retroarc of the Southern Andes between 38° and 40°S is formed by a NNW-elongated ridge not associated with stacked thrust sheets. On the contrary, during the last 4-3 Ma this ridge was affected by extensional deformation, regional uplift and related folding on a very broad scale. Receiver function analysis shows that the drainage divide area and adjacent retroarc lie over an attenuated crust. Normal crustal thickness at these latitudes is around 42km, whereas in this part of the retroarc the thickness is less than 32km. The causes for such attenuation have been linked to a moderate steepening of the subducted Nazca plate beneath South American plate, which is suggested by a westward shift and narrowing of the arc during the last 5Ma

  14. Gravity Anomalies and Depths of Sedimentary of Mekong Delta Area, South of Vietnam

    NASA Astrophysics Data System (ADS)

    Dang Van, L.

    2014-12-01

    The Mekong Delta is the region in the south of Vietnam with the total area of about 40.000 km2 and almost of this area is covered by water. Gravity measurement of this area was performed by Cuu Long Petroleum Agency (Vietnam) in 1980's and the Bouguer anomaly map of this area at the scale of 1/500.000 was established.We used the Bouguer anomaly map to study the geological structure of this area. This paper is divided into two parts. Firstly, we split the Mekong Delta area into two basins (CanTho-DongThap and TraCu basins) and two swells (Saigon and SocTrang swells) and delineated their boundaries by using the characteristics of Bouguer anomalies. Secondly, we used the second polynomial formula to separate the Bouger anomaly map into the regional and residual gravity anomaly maps. With this residual anomaly map, the 3D basemenf of Cenozoic-Mesozoic sediments of this area was computed by using the Parker-Oldenburg method.

  15. Upward Continuation Apply Newly to Process Gravity Anomaly Data in the East China Sea

    NASA Astrophysics Data System (ADS)

    Han, Bo; Zhang, Xunhua; Jiang, Jinyu

    2014-05-01

    The research area lies in the East China Sea and its adjacent area and the concrete is between 120-130 degree of east longitude and 20-30 degree of north latitude and it also lies between Eurasian Plate and Pacific Plate. The structures of the area transform differently and they are namely Uplifted Zone of Zhejiang-Fujian, East China Sea Shelf Basin, Okinawa Trough Back-arc Basin, Ryukyu Arc, Ryukyu trench and Philippine Sea from west to east. Bouguer gravity anomaly can reflect deep structure characters and it is help to judge deep structures. The bouguer gravity anomalies of the area change differently from west to east. The anomalies increase gradually from land to the middle of Okinawa trough and near land anomaly contour strike accords with coastline and the middle of Okinawa trough reflect the highest anomalies in this area. Gravity anomalies re-increase from Ryukyu fore-arc basin to trench and Ryukyu island arc appears the low anomalies. Philippine Sea appears high gravity anomalies background. Upward continuation method has been used to process original gravity anomaly as a common method and its destination is to weaken local anomaly and at last strengthen deep anomaly and it's important to deep structure study. Upward 5 km, 10 km and 20 km have been used to process data and the results been compared. However, the research area is very large and the deep structure is complex, it isn't suitable to use single height to upward continuation processing bouguer gravity anomaly. Then we propose multiple upward heights continuation to process gravity data respectively in different area. We use upward 20km to process data in the area from land to the slope and upward 10km from Okinawa trough to Ryukyu island arc and upward 5km from Ryukyu trench to Philippine Sea. At last we obtain multiple upward height result and the calculated result confirms that it is fit to use this method. Gravity anomalies contours become smoother than before and the deep structures become

  16. Interpretation of gravity anomalies in the northwest Adirondack lowlands, northern New York

    SciTech Connect

    Revetta, F.A.; O'Brian, B. . Geology Dept.)

    1993-03-01

    Twelve hundred gravity measurements were made in the Adirondack Highlands and northwest Adirondack Lowlands, New York between 44[degree]15 minutes and 44[degree]30 minutes N. Latitude and 75[degree]00 minutes W. Longitude. A Bouguer gravity map constructed from the gravity measurements includes the Carthage-Colton Mylonite Zone, a major structural boundary between the highlands and lowlands. The gravity map indicates the gravity contours trend parallel to the CCMZ along most of its length however in some areas the contours cross the boundary. No clear-cut relationships exists between the CCMZ and gravity contours. The Bouguer gravity map shows several prominent gravity anomalies which correlate with the geology seismicity and mineral deposits in the area. Gravity lows of 20 to 30 g.u. are centered over the Gouverneur, Hyde and Payne Lake Alaskite gneiss bodies. A gravity high of 20 g.u. occurs over the Pleasant Lake gabbro pluton. Gravity highs of 35 and 100 g.u. occur over the Sylvia Lake Zinc District and marble just north of the district. A gravity high at Russell, N.Y. coincides with a cluster of nine earthquake epicenters. Finally a steep gravity gradient separates high density rocks from lower density rocks along the Black Lake fault. Two-dimensional computer modeling of the geologic features is underway and quantitative models of the structures will be presented.

  17. Spreading rate dependence of gravity anomalies along oceanic transform faults.

    PubMed

    Gregg, Patricia M; Lin, Jian; Behn, Mark D; Montési, Laurent G J

    2007-07-12

    Mid-ocean ridge morphology and crustal accretion are known to depend on the spreading rate of the ridge. Slow-spreading mid-ocean-ridge segments exhibit significant crustal thinning towards transform and non-transform offsets, which is thought to arise from a three-dimensional process of buoyant mantle upwelling and melt migration focused beneath the centres of ridge segments. In contrast, fast-spreading mid-ocean ridges are characterized by smaller, segment-scale variations in crustal thickness, which reflect more uniform mantle upwelling beneath the ridge axis. Here we present a systematic study of the residual mantle Bouguer gravity anomaly of 19 oceanic transform faults that reveals a strong correlation between gravity signature and spreading rate. Previous studies have shown that slow-slipping transform faults are marked by more positive gravity anomalies than their adjacent ridge segments, but our analysis reveals that intermediate and fast-slipping transform faults exhibit more negative gravity anomalies than their adjacent ridge segments. This finding indicates that there is a mass deficit at intermediate- and fast-slipping transform faults, which could reflect increased rock porosity, serpentinization of mantle peridotite, and/or crustal thickening. The most negative anomalies correspond to topographic highs flanking the transform faults, rather than to transform troughs (where deformation is probably focused and porosity and alteration are expected to be greatest), indicating that crustal thickening could be an important contributor to the negative gravity anomalies observed. This finding in turn suggests that three-dimensional magma accretion may occur near intermediate- and fast-slipping transform faults. PMID:17625563

  18. Deformation induced topographic effects in inversion of temporal gravity changes: First look at Free Air and Bouguer terms

    NASA Astrophysics Data System (ADS)

    Vajda, Peter; Zahorec Pavol, Pavol; Papčo, Juraj; Kubová, Anna

    2015-06-01

    We review here the gravitational effects on the temporal (time-lapse) gravity changes induced by the surface deformation (vertical displacements). We focus on two terms, one induced by the displacement of the benchmark (gravity station) in the ambient gravity field, and the other imposed by the attraction of the masses within the topographic deformation rind. The first term, coined often the Free Air Effect (FAE), is the product of the vertical gradient of gravity (VGG) and the vertical displacement of the benchmark. We examine the use of the vertical gradient of normal gravity, typically called the theoretical or normal Free Air Gradient (normal FAG), as a replacement for the true VGG in the FAE, as well as the contribution of the topography to the VGG. We compute a topographic correction to the normal FAG, to offer a better approximation of the VGG, and evaluate its size and shape (spatial behavior) for a volcanic study area selected as the Central Volcanic Complex (CVC) on Tenerife, where this correction reaches 77% of the normal FAG and varies rapidly with terrain. The second term, imposed by the attraction of the vertically displaced topo-masses, referred to here as the Topographic Deformation Effect (TDE) must be computed by numerical evaluation of the Newton volumetric integral. As the effect wanes off quickly with distance, a high resolution DEM is required for its evaluation. In practice this effect is often approximated by the planar or spherical Bouguer deformation effect (BDE). By a synthetic simulation at the CVC of Tenerife we show the difference between the rigorously evaluated TDE and its approximation by the planar BDE. The complete effect, coined here the Deformation Induced Topographic Effect (DITE) is the sum of FAE and TDE. Next we compare by means of synthetic simulations the DITE with two approximations of DITE typically used in practice: one amounting only to the first term in which the VGG is approximated by normal FAG, the other adopting a

  19. Thickness variation of the sedimentary cover in the South Western Desert of Egypt as deduced from Bouguer gravity and drill-hole data using neural network method

    NASA Astrophysics Data System (ADS)

    Abdel Zaher, M.; Senosy, M. M.; Youssef, M. M.; Ehara, S.

    2009-06-01

    The Bouguer anomaly map of scale 1:500,000 and the lithological logs of more than 120 deep wells distributed in the Southern part of Western Desert of Egypt were used to determine the thickness of the sedimentary cover containing the main sandstone water formation. The predominant structures affecting both the basement rock and the sedimentary cover were also studied. Gravity stripping approach was applied to separate density anomalies within the sedimentary fill from the influence of deeper levels in the crystalline crust. The study indicated that the surface of the basement rock is highly rugged and mostly controlled by structures causing variation of the sedimentary cover thickness from location to other all over the area. Isopach maps were constructed based on the Artificial Neural Network (ANN) model which is considered a best method for that operation. The maximum thickness of sandstone formations is recorded at west Oweinat, southwest of Aswan, Dakhla oasis and west of Qena town. As this formation is the main water aquifer in the study area, therefore these locations are characterized by the presence of huge amount of ground water. Accordingly, these areas must be taking the priority in the programs of sustainable development in southern Egypt.

  20. Bouguer Images of the North American Craton

    NASA Technical Reports Server (NTRS)

    Arvidson, R. E.; Bindschadler, D.; Bowring, S.; Eddy, M.; Guinness, E.; Leff, C.

    1985-01-01

    Processing of existing gravity and aeromagnetic data with modern methods is providing new insights into crustal and mantle structures for large parts of the United States and Canada. More than three-quarters of a million ground station readings of gravity are now available for this region. These data offer a wealth of information on crustal and mantle structures when reduced and displayed as Bouguer anomalies, where lateral variations are controlled by the size, shape and densities of underlying materials. Digital image processing techniques were used to generate Bouguer images that display more of the granularity inherent in the data as compared with existing contour maps. A dominant NW-SE linear trend of highs and lows can be seen extending from South Dakota, through Nebaska, and into Missouri. This trend is probably related to features created during an early and perhaps initial episode of crustal assembly by collisional processes. The younger granitic materials are probably a thin cover over an older crust.

  1. New Antarctic gravity anomaly grid for enhanced geodetic and geophysical studies in Antarctica

    NASA Astrophysics Data System (ADS)

    Scheinert, M.; Ferraccioli, F.; Schwabe, J.; Bell, R.; Studinger, M.; Damaske, D.; Jokat, W.; Aleshkova, N.; Jordan, T.; Leitchenkov, G.; Blankenship, D. D.; Damiani, T. M.; Young, D.; Cochran, J. R.; Richter, T. D.

    2016-01-01

    Gravity surveying is challenging in Antarctica because of its hostile environment and inaccessibility. Nevertheless, many ground-based, airborne, and shipborne gravity campaigns have been completed by the geophysical and geodetic communities since the 1980s. We present the first modern Antarctic-wide gravity data compilation derived from 13 million data points covering an area of 10 million km2, which corresponds to 73% coverage of the continent. The remove-compute-restore technique was applied for gridding, which facilitated leveling of the different gravity data sets with respect to an Earth gravity model derived from satellite data alone. The resulting free-air and Bouguer gravity anomaly grids of 10 km resolution are publicly available. These grids will enable new high-resolution combined Earth gravity models to be derived and represent a major step forward toward solving the geodetic polar data gap problem. They provide a new tool to investigate continental-scale lithospheric structure and geological evolution of Antarctica.

  2. Complete Bouguer gravity map of the Nevada Test Site and vicinity, Nevada

    SciTech Connect

    Healey, D.L.; Harris, R.N.; Ponce, D.A.; Oliver, H.W.

    1987-12-31

    About 15,000 gravity stations were used to create the gravity map. Gravity studies at the Nevada Test Site were undertaken to help locate geologically favorable areas for underground nuclear tests and to help characterize potential high-level nuclear waste storage sites. 48 refs. (TEM)

  3. Gravity anomalies, spatial variation of flexural rigidity, and role of inherited crustal structure in the Aquitaine Basin

    NASA Astrophysics Data System (ADS)

    Angrand, Paul; Ford, Mary; Watts, Anthony; Bell, Rebecca E.

    2016-04-01

    The Aquitaine foreland basin developed from Campanian to Miocene by flexure of the upper (European) plate during the Pyrenean orogeny. The foreland basin forms a syn-orogenic sedimentary wedge up to 6 km thick in the south, thinning rapidly north and has a maximum width of 200 km in the west. The flexural basin was superimposed on a lithosphere previously affected by Apto-Albian hyper-extension. What are the effects of an inherited extremely weak and narrow rifted zone on the behavior of a superimposed flexural foreland basin? Coupled with surface and subsurface data, Bouguer gravity anomalies were used to determine the crustal structure of the northern Pyrenean retrowedge and the flexure of the European plate. In the centre, the basin shows a regional Bouguer anomaly pattern typical of foreland basins with the maximum of syn-orogenic deposits corresponding to a low and the forebulge to a high. However, south of the North Pyrenean Frontal Thrust (NPFT) this regional field is overprinted by strong positive Bouguer anomalies, which correspond to high density bodies (mantle or lower crust) transported along the NPFT. Stratigraphy shows that the central basin evolved as a series of narrow, laterally variable depocentres that migrated north. Shortening is accommodated mainly by thick skinned deformation and local reactivation of salt structures. In the east, the Toulouse Fault separates the central and eastern foreland. The eastern foreland shows a broader zone of negative Bouguer values. This foreland is salt-free and stratigraphy records higher subsidence. The easternmost basin is completely overprinted by the opening of the Gulf of Lion. In the west, the foreland does not show a typical regional gravity anomaly pattern due to overprinting by the opening of the Bay of Biscay. Instead, a major gravity high is centered on the northern Landes High, with a second high centered on the Labourd massif south of the NPFT. Neither the Parentis rift basin nor the salt

  4. Consistent anomalies of the induced W gravities

    NASA Astrophysics Data System (ADS)

    Abud, Mario; Ader, Jean-Pierre; Cappiello, Luigi

    1996-02-01

    The BRST anomaly which may be present in the induced Wn gravity quantized on the light-cone is evaluated in the geometrical framework of Zucchini. The cocycles linked by the cohomology of the BRST operator to the anomaly are straightforwardly calculated thanks to the analogy between this formulation and the Yang-Mills theory. We give also a conformally covariant formulation of these quantities including the anomaly, which is valid on arbitrary Riemann surfaces. The example of the W3 theory is discussed and a comparison with other candidates for the anomaly available in the literature is presented.

  5. Gravity and magnetic anomalies of the Cyprus arc and tectonic implications

    NASA Astrophysics Data System (ADS)

    Ergün, M.; Okay, S.; Sari, C.; Oral, E. Z.

    2003-04-01

    In present day, eastern Mediterranean is controlled by the collision of the African and Eurasian plates and displacements of Arabian, Anatolian and Aegean micro-plates. The boundary between African and Eurasian plates is delineated by the Hellenic arc and Pliny-Strabo trench in the west and the Cyprus arc and a diffuse fault system of the Eastern Anatolian Fault zone in the east. The available gravity and magnetic data from the easternmost Mediterranean allow to subdivide this basin into three provinces: the northeastern Mediterranean north of the Cyprus Arc; the Levant Basin south of the Cyprus Arc and east of the line that roughly continues the Suez rift trend toward the Gulf of Antalya, between Cyprus and Anaximander Mountains; and the Mediterranean Ridge, Herodotus Basin west of this line. High anomalies observed in Cyprus and the sea region at the south is prominent in the gravity data. The Bouguer gravity anomaly reaches its maximum values over Cyprus, where it is most probably caused by high dense Troodos ophiolites. The uplifted oceanic crust causes high Bouguer anomaly also seen in the vicinity of Eratosthenes Seamount. Another result obtained from gravity data is that the crust under Herodotos and Rhodes basins is somehow oceanic and Anaximander, Eratosthenes and Cyprus are continental fragments. There are no linear magnetic anomalies in the Mediterranean. But there are magnetic anomalies over the Eratosthenes seamount and as well as from Cyprus to the Antalya basin due to the ophiolitic bodies. In Cyprus, the last compressional deformations were defined near the Miocene/Pliocene boundary. The extensional deformation associated with the Antalya basin appears to be separated by a zone of the Florence rise and Anaximander Mountains affected by differential tectonic movements. Eratosthenes Seamount is a positive crustal feature in the process of collision with Cyprus along an active margin; there is clearly a potential tectonic relationship to the onland

  6. Newberry Combined Gravity 2016

    DOE Data Explorer

    Kelly Rose

    2016-01-22

    Newberry combined gravity from Zonge Int'l, processed for the EGS stimulation project at well 55-29. Includes data from both Davenport 2006 collection and for OSU/4D EGS monitoring 2012 collection. Locations are NAD83, UTM Zone 10 North, meters. Elevation is NAVD88. Gravity in milligals. Free air and observed gravity are included, along with simple Bouguer anomaly and terrain corrected Bouguer anomaly. SBA230 means simple Bouguer anomaly computed at 2.30 g/cc. CBA230 means terrain corrected Bouguer anomaly at 2.30 g/cc. This suite of densities are included (g/cc): 2.00, 2.10, 2.20, 2.30, 2.40, 2.50, 2.67.

  7. Crustal Thickness on the Mid-Atlantic Ridge: Bull's-Eye Gravity Anomalies and Focused Accretion.

    PubMed

    Tolstoy, M; Harding, A J; Orcutt, J A

    1993-10-29

    Spreading segments of the Mid-Atlantic Ridge show negative bull's-eye anomalies in the mantle Bouguer gravity field. Seismic refraction results from 33 degrees S indicate that these anomalies can be accounted for by variations in crustal thickness along a segment. The crust is thicker in the center and thinner at the end of the spreading segment, and these changes are attributable to variations in the thickness of layer 3. The results show that accretion is focused at a slow-spreading ridge, that axial valley depth reflects the thickness of the underlying crust, and that along-axis density variations should be considered in the interpretation of gravity data. PMID:17812339

  8. Magnetic and gravity anomalies in the Americas

    NASA Technical Reports Server (NTRS)

    Braile, L. W.; Hinze, W. J.; Vonfrese, R. R. B. (Principal Investigator)

    1981-01-01

    The cleaning and magnetic tape storage of spherical Earth processing programs are reported. These programs include: NVERTSM which inverts total or vector magnetic anomaly data on a distribution of point dipoles in spherical coordinates; SMFLD which utilizes output from NVERTSM to compute total or vector magnetic anomaly fields for a distribution of point dipoles in spherical coordinates; NVERTG; and GFLD. Abstracts are presented for papers dealing with the mapping and modeling of magnetic and gravity anomalies, and with the verification of crustal components in satellite data.

  9. Gravity anomaly detection: Apollo/Soyuz

    NASA Technical Reports Server (NTRS)

    Vonbun, F. O.; Kahn, W. D.; Bryan, J. W.; Schmid, P. E.; Wells, W. T.; Conrad, D. T.

    1976-01-01

    The Goddard Apollo-Soyuz Geodynamics Experiment is described. It was performed to demonstrate the feasibility of tracking and recovering high frequency components of the earth's gravity field by utilizing a synchronous orbiting tracking station such as ATS-6. Gravity anomalies of 5 MGLS or larger having wavelengths of 300 to 1000 kilometers on the earth's surface are important for geologic studies of the upper layers of the earth's crust. Short wavelength Earth's gravity anomalies were detected from space. Two prime areas of data collection were selected for the experiment: (1) the center of the African continent and (2) the Indian Ocean Depression centered at 5% north latitude and 75% east longitude. Preliminary results show that the detectability objective of the experiment was met in both areas as well as at several additional anomalous areas around the globe. Gravity anomalies of the Karakoram and Himalayan mountain ranges, ocean trenches, as well as the Diamantina Depth, can be seen. Maps outlining the anomalies discovered are shown.

  10. Isostatic models and isostatic gravity anomalies of the Arabian plate and surroundings

    NASA Astrophysics Data System (ADS)

    Kaban, Mikhail K.; El Khrepy, Sami; Al-Arifi, Nassir

    2015-04-01

    Isostaic anomalies represent one of the most useful "geological" reduction of the gravity field. With the isostatic correction it is possible to remove a significant part of the effect of deep density heterogeneity, which dominates in the Bouguer gravity anomalies. This correction is based on the fact that a major part of the near-surface load is compensated by variations of the lithosphere boundaries (chiefly the Moho and LAB) and by density variations within the crust and upper mantle. It is usually supposed that it is less important to a first order, what is the actual compensation model when reducing the effect of compensating masses, since their total weight is exactly opposite to the near-surface load. We compare several compensating models for the Arabian plate and surrounding area. The Airy model gives very significant regional isostatic anomalies, which can not be explained by the upper crust structure or disturbances of the isostatic equilibrium. Also the predicted "isostatic" Moho is very different from the existing observations. The second group of the isostatic models includes the Moho, which is based on existing seismic determinations. Additional compensation is provided by density variations within the lithosphere (chiefly in the upper mantle). In this way we minimize regional anomalies over the Arabian plate. The residual local anomalies well correspond to tectonic structure of the plate. Still very significant anomalies are associated with the Zagros fold belt, the collision zone of the Arabian and Eurasian plates.

  11. Gravity and magnetic anomaly data analysis

    NASA Technical Reports Server (NTRS)

    Braile, L. W.; Hinze, W. J.; Vonfrese, R. R. B. (Principal Investigator)

    1982-01-01

    Progress on the analysis MAGSAT data is reported. The MAGSAT data from 40 deg S to 70 deg N latitude and 30 deg W to 60 E longitude was reduced to radial polarization. In addition, gravity anomaly data from this area were processed and a variety of filtered maps were prepared for combined interpretation of the gravity and magnetic data in conjunction with structural and tectonic maps of the area. The VERSATEC listings and cross-reference maps of variable and array names for the spherical Earth analysis programs NVERTSM, SMFLD, NVERTG, and GFLD were also prepared.

  12. The Origin of the Rodrigues Depth Anomaly: New constraints from integrated gravity inversion

    NASA Astrophysics Data System (ADS)

    Minakov, Alexander; Gaina, Carmen; Faleide, Jan Inge

    2016-04-01

    This study is focused on the Western Indian Ocean including the Central Indian Ridge. The Rodrigues Ridge is a bathymetric feature (500 km -long and 20 km -wide) situated east of the Mascarene Plateau and Mauritius, with an oblique trend with respect to the underlying seafloor spreading fabric. The trend is also different from the fracture zone and hotspot tracks in this area. The region where the Rodrigues Ridge intersects the Central Indian Ridge is characterized by broad area being shallower than it should be according to standard age-depth relations for oceanic basement. With this contribution we aim to determine key factors controlling the formation of the Rodrigues Ridge and the development of the depth anomaly through time. In order to better constrain the nature and extent of the depth anomaly underlying the Rodrigues Ridge and surrounding region, we have carried out a 3D gravity and bathymetry data analysis. This analysis included an iterative gravity inversion approach linked to the computation of residual topography through the temperature and density model of the crust and upper mantle. We use a refined plate kinematic model of the study area for the time period ca. 30 Ma to the present. The refined kinematic model is an important element for temperature modelling at the ridge-transform intersection. Existing seismological data provide additional constraints for the gravity inversion. The results of the 3D gravity and bathymetry data analysis support the model of enhanced production of crust at the Central Indian Ridge adjacent to the Rodrigues Ridge. The depth anomaly is composed of abrupt Rodrigues Ridge edifice sitting on top a relatively smooth and broad anomaly characterized by crustal thickness between 8 and 13 km. These values are significantly higher than those typical for the crustal thickness generated by slow seafloor spreading at the Central Indian Ridge and other slow spreading ridges. This gives rise to a large negative residual mantle

  13. Trace anomaly and counterterms in designer gravity

    NASA Astrophysics Data System (ADS)

    Anabalón, Andrés; Astefanesei, Dumitru; Choque, David; Martínez, Cristián

    2016-03-01

    We construct concrete counterterms of the Balasubramanian-Kraus type for Einstein-scalar theories with designer gravity boundary conditions in AdS4, so that the total action is finite on-shell and satisfy a well defined variational principle. We focus on scalar fields with the conformal mass m 2 = -2 l -2 and show that the holographic mass matches the Hamiltonian mass for any boundary conditions. We compute the trace anomaly of the dual field theory in the generic case, as well as when there exist logarithmic branches of non-linear origin. As expected, the anomaly vanishes for the boundary conditions that are AdS invariant. When the anomaly does not vanish, the dual stress tensor describes a thermal gas with an equation of state related to the boundary conditions of the scalar field. In the case of a vanishing anomaly, we recover the dual theory of a massless thermal gas. As an application of the formalism, we consider a general family of exact hairy black hole solutions that, for some particular values of the parameters in the moduli potential, contains solutions of four-dimensional gauged {N}=8 supergravity and its ω-deformation. Using the AdS/CFT duality dictionary, they correspond to triple trace deformations of the dual field theory.

  14. Determination of mean gravity anomalies in the Taiwan Island

    NASA Technical Reports Server (NTRS)

    Chang, Ruey-Gang

    1989-01-01

    The fitting and proper regression coefficients were made of one hundred seventeen 10 x 10' blocks with observed gravity data and corresponding elevation in the Taiwan Island. To compare five different predicted models, and the proper one for the mean gravity anomalies were determined. The predicted gravity anomalies of the non-observed gravity blocks were decided when the coefficients obtained through the model with the weighted mean method. It was suggested that the mean gravity anomalies of 10 x 10' blocks should be made when comprehensive the observed and predicted data.

  15. Tertiary basin-and-range structure in Southern Nevada-Utah-Arizona region via borehole, seismic reflection, and Bouguer gravity data: Insights on hydrocarbon potential

    SciTech Connect

    Carpenter, D.G.

    1988-01-01

    Extension characterized by full grabens and half-grabens and tilted, folded, and faulted range blocks is geometrically and kinematically constrained by geologic and geophysical data. Rootless gravity-slide blocks are common secondary features to high-angle normal faults, which exert primary control over crustal extension. A synthetic seismogram from the only test well (Mobil Virgin River 1-A; TD = 5,962.5m), seismic reflection, and Bouguer gravity data (up to 70 mgal of relief) indicate over 7,600m of low-density Tertiary sediments in the Virgin Valley basin. Several thousand meters of sediment are within the oil-generative window. Neogene basalt flows suggest geothermal gradients higher than today. Lacustrine limestone in the Oliocene-Miocene Horse Spring Formation contains cryptalgalaminate, a potential hydrocarbon source. The Horse Spring Formation is overlain unconformably by the Miocene-Pliocene Muddy Creek Formation. These formations were deposited in association with movement on the Virgin-Beaver Dam Mountains fault, as indicated by fanning-upward reflector geometry. The formations are incorporated into a major rollover anticline. Mississippian Chainman Shale, penetrated to the west by Chevron's Colorock Quarry well, indicates a possibility for Sevier-age hydrocarbon generation by thrust loading.

  16. Spectral analysis of gravity anomalies and the architecture of tectonic wedging, NE Venezuela and Trinidad

    NASA Astrophysics Data System (ADS)

    Russo, R. M.; Speed, R. C.

    1994-06-01

    We have analyzed the spectral content of free air gravity anomalies in the Caribbean-South American plate boundary zone in order to determine better the near-surface (0-120 km) distribution of crustal and upper mantle elements which give rise to the unusual gravity field of this region. The plate boundary zone in northeastern Venezuela and Trinidad is the site of the world's sea level continental minimum of Bouguer gravity anomalies, yet the region is also one of mild topography (mean value 43 m, maximum 1200 m). We find the mean depths to interfaces of significant density contrast at a variety of depths for portions of the plate boundary zone. We interpret interfaces at 30-35 km and 32 km beneath the Guyana Shield and the Aves Ridge, respectively, to be the Moho. Other shallow interfaces (5-14 km) are most likely sediment cover-basement contacts in the Maturin foreland basin and southern Grenada Basin. Deeper interfaces (54-63 km) we associate with loaded and downwarped continental and oceanic South American lithosphere. The deepest boundaries, at depths of 89-120 km, may be related to detached or detaching oceanic lithosphere overridden by continental South America. We use our results to test the tectonic wedging model of the plate boundary zone recently published by Russo and Speed (1992). We find that the tectonic wedging model adequately describes many of the structural boundaries inferable from our analysis of gravity anomalies but that the model must be modified to include a thinner Guyana Shield crust.

  17. Isostatic Model and Isostatic Gravity Anomalies of the Arabian Plate and Surroundings

    NASA Astrophysics Data System (ADS)

    Kaban, Mikhail K.; El Khrepy, Sami; Al-Arifi, Nassir

    2016-04-01

    The isostatic modeling represents one of the most useful "geological" reduction methods of the gravity field. With the isostatic correction, it is possible to remove a significant part of the effect of deep density heterogeneity, which dominates in the Bouguer gravity anomalies. Although there exist several isostatic compensation schemes, it is usually supposed that a choice of the model is not an important factor to first order, since the total weight of compensating masses remains the same. We compare two alternative models for the Arabian plate and surrounding area. The Airy model gives very significant regional isostatic anomalies, which cannot be explained by the upper crust structure or disturbances of the isostatic equilibrium. Also, the predicted "isostatic" Moho is very different from existing seismic observations. The second isostatic model includes the Moho, which is based on seismic determinations. Additional compensation is provided by density variations within the lithosphere (chiefly in the upper mantle). According to this model, the upper mantle under the Arabian Shield is less dense than under the Platform. In the Arabian platform, the maximum density coincides with the Rub' al Khali, one of the richest oil basin in the world. This finding agrees with previous studies, showing that such basins are often underlain by dense mantle, possibly related to an eclogite layer that has caused their subsidence. The mantle density variations might be also a result of variations of the lithosphere thickness. With the combined isostatic model, it is possible to minimize regional anomalies over the Arabian plate. The residual local anomalies correspond well to tectonic structure of the plate. Still very significant anomalies, showing isostatic disturbances of the lithosphere, are associated with the Zagros fold belt, the collision zone of the Arabian and Eurasian plates.

  18. Upgraded gravity anomaly base of the United States

    USGS Publications Warehouse

    Keller, Gordon R.; Hildenbrand, T.G.; Kucks, R.; Roman, D.; Hittelman, A.M.

    2002-01-01

    A concerted effort to compile an upgraded gravity anomaly database, grid, and map for the United States by the end of 2002 is under way. This effort can be considered as the first step in building a data system for gravity measurements, and it builds on existing collaborative efforts. This paper outlines the strategy for assembling the individual map and digital products related to the United States gravity database.

  19. Validation of South American terrestrial gravity anomalies by GOCE

    NASA Astrophysics Data System (ADS)

    Fecher, Thomas; Pail, Roland; Gruber, Thomas; Holmes, Simon

    2015-04-01

    Since its launch in 2009, ESA's GOCE mission has generated high-accuracy gravity field information, of near-global coverage, for the long- to medium-wavelength part of the gravity field (<=degree/order 260). These highly accurate gravity data are especially important for regions such as South America, Africa or Asia, where coverage and/or accuracy of alternate data sets, mostly gravimetry, are relatively poor. In these regions, the GOCE data can be useful in identifying and assessing suspect terrestrial data. Specifically, in coordination with partner organizations, we are already leveraging satellite gravity field missions to identify inconsistencies between different regional gravity anomaly data sets. Many of these inconsistencies relate to data quality issues. Resolving these issues better enables the terrestrial gravity data to strengthen and correct the satellite gravity models at their higher end (degree/order 200 to 260). The harmonization between terrestrial and satellite datasets reduces the commission error in gravity modeling over the associated range. Remaining issues not related to data quality can then be isolated for additional study. For example, a host of geophysical and temporal issues may be contributing to irregularities. In this paper, the quality of a South America data set of gravity anomalies shall be analyzed. The accuracy of the gravity anomalies shall be assessed, and systematic errors shall be detected. For this purpose, consistent gravity field corrections have to be applied. The aim of the revision of the data set is to exclude bad data and to provide accuracies which can serve as a stochastic model in the frame of a combined solution. By this procedure, the performance of a gravity field model based on the combination of satellite and terrestrial observations should be improved for South America.

  20. Spectral Correlation of Antarctic Satellite Magnetic and Gravity Anomalies

    NASA Astrophysics Data System (ADS)

    Wells, S. B.; von Frese, R. R.; Kim, H.; Potts, L.; Kim, J.; Gaya-Pique, L. R.

    2005-05-01

    Large areas of the Antarctic continent lack terrestrial or airborne magnetic and gravity survey coverage due to the harsh climate and extended distances involved. Satellite missions therefore play an important role, often being the only source of information for the study of remote regions. NASA's GRACE satellite mission provides global-scale gravity measurements with a much higher spatial resolution than previous missions. The free-air gravity anomalies in Antarctica from GRACE offer new insights on the poorly understood Antarctic crust. New interpretations and candidates for further investigation are presented from spectral correlation analysis between the new GRACE free-air gravity anomalies and magnetic anomalies measured by the CHAMP and Ørsted satellites. We quantify the anomaly correlations using correlation filters based on Poisson's relation. Favorability indices are derived that highlight the positive and negative correlations between the satellite observed geopotential anomalies. Several positively and negatively correlated regional anomalies yield new insights on the enigmatic crustal tectonics of Queen Maud Land, Enderby Land and other regions of East Antarctica, and the West Antarctic Peninsula.

  1. Detailed gravity anomalies from GEOS-3 satellite altimetry data

    NASA Technical Reports Server (NTRS)

    Gopalapillai, G. S.; Mourad, A. G.

    1978-01-01

    A technique for deriving mean gravity anomalies from dense altimetry data was developed. A combination of both deterministic and statistical techniques was used. The basic mathematical model was based on the Stokes' equation which describes the analytical relationship between mean gravity anomalies and geoid undulations at a point; this undulation is a linear function of the altimetry data at that point. The overdetermined problem resulting from the excessive altimetry data available was solved using Least-Squares principles. These principles enable the simultaneous estimation of the associated standard deviations reflecting the internal consistency based on the accuracy estimates provided for the altimetry data as well as for the terrestrial anomaly data. Several test computations were made of the anomalies and their accuracy estimates using GOES-3 data.

  2. Study of gravity and magnetic anomalies using MAGSAT data

    NASA Technical Reports Server (NTRS)

    Braile, L. W.; Hinze, W. J.; Vonfrese, R. R. B. (Principal Investigator)

    1981-01-01

    The results of modeling satellite-elevation magnetic and gravity data using the constraints imposed by near surface data and seismic evidence shows that the magnetic minimum can be accounted for by either an intracrustal lithologic variation or by an upwarp of the Curie point isotherm. The long wavelength anomalies of the NOO's-vector magnetic survey of the conterminous U.S. were contoured and processed by various frequency filters to enhance particular characteristics. A preliminary inversion of the data was completed and the anomaly field calculated at 450 km from the equivalent magnet sources to compare with the POGO satellite data. Considerable progress was made in studing the satellite magnetic data of South America and adjacent marine areas. Preliminary versions of the 1 deg free-air gravity anomaly map (20 m gal contour interval) and the high cut (lambda approximately 8 deg) filtered anomaly maps are included.

  3. Approximating edges of source bodies from magnetic or gravity anomalies.

    USGS Publications Warehouse

    Blakely, R.J.; Simpson, R.W.

    1986-01-01

    Cordell and Grauch (1982, 1985) discussed a technique to estimate the location of abrupt lateral changes in magnetization or mass density of upper crustal rocks. The final step of their procedure is to identify maxima on a contoured map of horizontal gradient magnitudes. Attempts to automate their final step. The method begins with gridded magnetic or gravity anomaly data and produces a plan view of inferred boundaries of magnetic or gravity sources. The method applies to both local surveys and to continent-wide compilations of magnetic and gravity data.-from Authors

  4. Magnetic and gravity anomalies of the slow-spreading system in the Gulf of Aden

    NASA Astrophysics Data System (ADS)

    Nakanishi, M.; Fujimoto, H.; Tamaki, K.; Okino, K.

    2002-12-01

    The spreading system in the Gulf of Aden between Somalia, NE Africa, and Arabia has an ENE-WSW trend and its half spreading rate is about 1.0 cm/yr (e.g., Jestin et al., 1994). Previous studies (e.g., Tamsett and Searle, 1988) provided the general morphology of the spreading system. To reveal detailed morphology and tectonics of the spreading system in the Gulf of Aden, geophysical investigation was conducted along the spreading system between 45°30OE and 50°20OE by the R/V Hakuho-maru from December 2000 to January 2001. Bathymetric data were collected using an echo sounder SEA BEAM 2120 aboard R/V Hakuho-maru. Magnetic and gravity data were collected by towed proton magnetometer and shipboard gravimeter, respectively. The strike of the spreading centers east of 46°30OE is N65°W. The topographic expression of the spreading centers east of N46°30OE is an axial rift valley offset by transform faults siilar to that observed at slow spreading centers in other areas. The bathymetric feature of the spreading centers between 45°50OE and 46°30OE with a strike N80°E is N65°W trending en-echelon basins. The spreading center west of 45°50OE with a strike E-W is bouned by linear ridges and its bathymetric expression is N65°W trending en-echelon ridges. The axial rift valley west of N46°30OE is not offset by any prominent transform faults. Negative magnetic anomaly is dominant over the axial valleys. Its amplitude is about 500 nT and the wavelength is about 30 km. Prominent linear negative magnetic anomaly, which is more than 1000 nT, exists west of N46°30OE. The strike of the linear magnetic anomaly correlates with that of axial valleys west of N46°30OE. Mantle Bouguer gravity anomaly of the spreading centers increases eastward. This trend correlates with the eastward deepening of spreading centers.

  5. Crustal structure and gravity anomalies beneath the Rif, northern Morocco: implications for the current tectonics of the Alboran region

    NASA Astrophysics Data System (ADS)

    Petit, Carole; Le Pourhiet, Laetitia; Scalabrino, Bruno; Corsini, Michel; Bonnin, Mickael; Romagny, Adrien

    2015-04-01

    We analyze Bouguer anomaly data and previously published Moho depths picked from receiver functions in order to determine the amount of isostatic compensation or un-compensation of the Rif topography in northern Morocco. We use Moho depth variations extracted from receiver function analyses to predict synthetic Bouguer anomalies that are then compared to observed Bouguer anomaly. We find that Moho depth variations due to isostatic compensation of topographic and/or intracrustal loads do not match Moho depth estimates obtained from receiver function analyses. The isostatic misfit map evidences excess crustal root as large as 15 km in the western part of the study area, whereas a "missing" crustal root appears east of 4.3°E. Given crustal thickness provided by reciever function data, we estimated the amount of "missing" topography (in a local isostatic sense) in the Western Rif at 1000±500 m depending on the assumed crust-mantle density contrast, i.e. twice to four times lower than the actual Rif highest elevation (>2000m). Therefore, without this negative dynamic effect, the Rif topography would be higher by 25% to 75% compared to its actual elevation. This excess root/ missing topography correlates with the presence of a dense mantle lid, the noticeable south-westward drift of the Western Rif area, and with a current surface uplift.Integrating gravity data, crustal thickness from reciever functions, seismic tomography, GPS and geologic models, we propose that local thickening of the crust corresponds to the dynamic response to the delaminated mantle lid that is progressively detaching westward or south-westward from the overlying crust. In this model, provided the lower crust is sufficiently buoyant and weak, the inward flow of lower crust towards the mantle hinge can cause a positive isostatic topography that is larger than the negative dynamic topography created by the sinking mantle lid. According to this hypothesis, the long wavelength Rif topography can be

  6. Gravity anomalies and deep structure of eastern Hudson bay

    NASA Astrophysics Data System (ADS)

    Mukhopadhyay, Manoj; Gibb, R. A.

    1981-01-01

    The Cape Smith and Belcher foldbelts of Lower Proterozoic (Aphebian) rocks form parts of the proposed Circum-Superior suture which separates the Superior and Churchill structural provinces of the Canadian Shield. Recent marine gravity surveys in eastern Hudson Bay (1976-1979) show that the distinctive linear gravity pattern of paired positive and negative anomalies along the Cape Smith foldbelt of northern Ungava extends southwards into Hudson Bay to the Belcher Islands. Interpretation of five gravity profiles across the Cape Smith and Belcher foldbelts suggests that the Churchill crust is thicker and denser than the Superior. The boundary between the two contrasting crustal blocks is interpreted as a collisional suture. The rocks of the foldbelts which are progressively more volcanic northwards are the source of a residual positive anomaly associated with the Cape Smith foldbelt and a series of discontinuous positive residual anomalies in the Bay. To the north the thicknesses of the foldbelt rocks are estimated to be between 4 and 9 km with a local maximum of 13 km in the northernmost profile. To the south in the Belcher Islands, where geological estimates of formation thickness and measured rock densities provide more constraints on the interpretation of the residual anomalies, the foldbelt rocks are generally 6-7 km thick with a local maximum thickness of about 9 km. One possible interpretation of paleomagnetic results for Belcher Islands rocks in terms of a two-plate model lends support to the collision hypothesis.

  7. Relationship between the regional tectonic activity and crustal structure in the eastern Tibetan plateau discovered by gravity anomaly

    NASA Astrophysics Data System (ADS)

    Xu, Xiao; Gao, Rui; Guo, Xiaoyu

    2016-04-01

    The eastern Tibetan plateau has been getting more and more attention because it combines active faults, uplifting, and large earthquakes together in a high-population region. Based on the previous researches, the most of Cenozoic tectonic activities were related to the regional structure of the local blocks within the crustal scale. Thus, a better understanding of the crustal structure of the regional tectonic blocks is an important topic for further study. In this paper, we combined the simple Bouguer gravity anomaly with the Moho depths from previous studies to investigate the crustal structure in this area. To highlight the crustal structures, the gravity anomaly caused by the Moho relief has been reduced by forward modeling calculations. A total horizontal derivative (THD) had been applied on the gravity residuals. The results indicated that the crustal gravity residual is compatible with the topography and the geological settings of the regional blocks, including the Sichuan basin, the Chuxiong basin, the Xiaojiang fault, and the Jinhe fault, as well as the Longmenshan fault zone. The THD emphasized the west margin of Yangtze block, i.e., the Longriba fault zone and the Xiaojiang fault cut through the Yangtze block. The checkboard pattern of the gravity residual in the Songpan-Garze fold belt and Chuandian fragment shows that the crust is undergoing a southward and SE-directed extrusion, which is coincident with the flowing direction indicated from the GPS measurements. By integrating the interpretations, the stepwise extensional mechanism of the eastern Tibetan plateau is supported by the southeastward crustal deformation, and the extrusion of Chuandian fragment is achieved by Xianshuihe fault.

  8. Gravity anomalies without geomagnetic disturbances interfere with pigeon homing--a GPS tracking study.

    PubMed

    Blaser, Nicole; Guskov, Sergei I; Entin, Vladimir A; Wolfer, David P; Kanevskyi, Valeryi A; Lipp, Hans-Peter

    2014-11-15

    The gravity vector theory postulates that birds determine their position to set a home course by comparing the memorized gravity vector at the home loft with the local gravity vector at the release site, and that they should adjust their flight course to the gravity anomalies encountered. As gravity anomalies are often intermingled with geomagnetic anomalies, we released experienced pigeons from the center of a strong circular gravity anomaly (25 km diameter) not associated with magnetic anomalies and from a geophysical control site, equidistant from the home loft (91 km). After crossing the border zone of the anomaly--expected to be most critical for pigeon navigation--they dispersed significantly more than control birds, except for those having met a gravity anomaly en route. These data increase the credibility of the gravity vector hypothesis. PMID:25392461

  9. On global gravity anomalies and two-scale mantle convection

    NASA Technical Reports Server (NTRS)

    Marsh, B. D.; Marsh, J. G.

    1976-01-01

    The two-scale model of mantle convection developed by Richter and Parsons (1975) predicts that if the depth of the convective layer is about 600 km, then for a plate moving at 10 cm/yr, longitudinal convective rolls will be produced in about 50 million years, and the strike of these rolls indicates the direction of motion of the plate relative to the upper mantle. The paper tests these predictions by examining a new global free air gravity model complete to the 30th degree and order. The free air gravity map developed shows a series of linear positive and negative anomalies (with transverse wavelengths of about 2000 km) spanning the Pacific Ocean, crossing the Pacific rise and striking parallel to the Hawaiian seamounts. It is suggested that the pattern of these anomalies may indicate the presence of longitudinal convective rolls beneath the Pacific plates, a result which tends to support the predictions of Richter and Parsons.

  10. New analytic solutions for modeling vertical gravity gradient anomalies

    NASA Astrophysics Data System (ADS)

    Kim, Seung-Sep; Wessel, Paul

    2016-05-01

    Modern processing of satellite altimetry for use in marine gravimetry involves computing the along-track slopes of observed sea-surface heights, projecting them into east-west and north-south deflection of the vertical grids, and using Laplace's equation to algebraically obtain a grid of the vertical gravity gradient (VGG). The VGG grid is then integrated via overlapping, flat Earth Fourier transforms to yield a free-air anomaly grid. Because of this integration and associated edge effects, the VGG grid retains more short-wavelength information (e.g., fracture zone and seamount signatures) that is of particular importance for plate tectonic investigations. While modeling of gravity anomalies over arbitrary bodies has long been a standard undertaking, similar modeling of VGG anomalies over oceanic features is not commonplace yet. Here we derive analytic solutions for VGG anomalies over simple bodies and arbitrary 2-D and 3-D sources. We demonstrate their usability in determining mass excess and deficiency across the Mendocino fracture zone (a 2-D feature) and find the best bulk density estimate for Jasper seamount (a 3-D feature). The methodologies used herein are implemented in the Generic Mapping Tools, available from gmt.soest.hawaii.edu.

  11. Gravity anomalies in Silurian pinnacle reef trend, southwestern Indiana

    SciTech Connect

    Malinconico, L.L. Jr.; Gognat, T.A.; Scher, P.L. )

    1989-08-01

    Structures produced over the top or along the margins of Silurian Pinnacle reefs have proven to be the source of significant oil production in the eastern Illinois basin. The authors have been able to refine gravity methods that can assist in the exploration of such reef targets. A gravity/density model was developed by combining the 1980 work of Dana at the Wilfred pool (Sullivan County, Indiana) with other lithologic and log data in southwestern Indiana. This model includes the density differences between the reef facies and surrounding lithologies as well as density variations that are the result of compaction of the sedimentary sequence above the reef. The density models suggest that positive gravity anomalies with amplitude between 1.5 to 2.5 mgals might occur over the reefs.

  12. Gravity survey of the southwestern part of the sourthern Utah geothermal belt

    SciTech Connect

    Green, R.T.; Cook, K.L.

    1981-03-01

    A gravity survey covering an area of 6200 km/sup 2/ was made over the southwestern part of the southern Utah geothermal belt. The objective of the gravity survey is to delineate the geologic structures and assist in the understanding of the geothermal potential of the area. A total of 726 new gravity stations together with 205 existing gravity stations, are reduced to give: (1) a complete Bouguer gravity anomaly map, and (2) a fourth-order residual gravity anomaly map; both maps have a 2-mgal contour interval. The complete Bouguer gravity anomaly map shows an east-trending regional gravity belt with a total relief of about 70 mgal which crosses the central portion of the survey area. The gravity belt is attributed to a crustal lateral density variation of 0.1 gm/cc from a depth of 5 to 15 km.

  13. The quest for the perfect gravity anomaly: Part 2 - Mass effects and anomaly inversion

    USGS Publications Warehouse

    Keller, Gordon R.; Hildenbrand, T.G.; Hinze, W. J.; Li, X.; Ravat, D.; Webring, M.

    2006-01-01

    Gravity anomalies have become an important tool for geologic studies since the widespread use of high-precision gravimeters after the Second World War. More recently the development of instrumentation for airborne gravity observations, procedures for acquiring data from satellite platforms, the readily available Global Positioning System for precise vertical and horizontal control, improved global data bases, and enhancement of computational hardware and software have accelerated the use of the gravity method. As a result, efforts are being made to improve the gravity databases that are made available to the geoscience community by broadening their observational holdings and increasing the accuracy and precision of the included data. Currently the North American Gravity Database as well as the individual databases of Canada, Mexico, and the United States of America are being revised using new formats and standards. The objective of this paper is to describe the use of the revised standards for gravity data processing and modeling and there impact on geological interpretations. ?? 2005 Society of Exploration Geophysicists.

  14. Altered Orientation and Flight Paths of Pigeons Reared on Gravity Anomalies: A GPS Tracking Study

    PubMed Central

    Blaser, Nicole; Guskov, Sergei I.; Meskenaite, Virginia; Kanevskyi, Valerii A.; Lipp, Hans-Peter

    2013-01-01

    The mechanisms of pigeon homing are still not understood, in particular how they determine their position at unfamiliar locations. The “gravity vector” theory holds that pigeons memorize the gravity vector at their home loft and deduct home direction and distance from the angular difference between memorized and actual gravity vector. However, the gravity vector is tilted by different densities in the earth crust leading to gravity anomalies. We predicted that pigeons reared on different gravity anomalies would show different initial orientation and also show changes in their flight path when crossing a gravity anomaly. We reared one group of pigeons in a strong gravity anomaly with a north-to-south gravity gradient, and the other group of pigeons in a normal area but on a spot with a strong local anomaly with a west-to-east gravity gradient. After training over shorter distances, pigeons were released from a gravitationally and geomagnetically normal site 50 km north in the same direction for both home lofts. As expected by the theory, the two groups of pigeons showed divergent initial orientation. In addition, some of the GPS-tracked pigeons also showed changes in their flight paths when crossing gravity anomalies. We conclude that even small local gravity anomalies at the birth place of pigeons may have the potential to bias the map sense of pigeons, while reactivity to gravity gradients during flight was variable and appeared to depend on individual navigational strategies and frequency of position updates. PMID:24194860

  15. Gravity anomalies, forearc morphology and seismicity in subduction zones

    NASA Astrophysics Data System (ADS)

    Bassett, D.; Watts, A. B.; Das, S.

    2012-12-01

    We apply spectral averaging techniques to isolate and remove the long-wavelength large-amplitude trench-normal topographic and free-air gravity anomaly "high" and "low" associated with subduction zones. The residual grids generated illuminate the short-wavelength structure of the forearc. Systematic analysis of all subduction boundaries on Earth has enabled a classification of these grids with particular emphasis placed on topography and gravity anomalies observed in the region above the shallow seismogenic portion of the plate interface. The isostatic compensation of these anomalies is investigated using 3D calculations of the gravitational admittance and coherence. In the shallow region of the megathrust, typically within 100 km from the trench, isolated residual anomalies with amplitudes of up to 2.5 km and 125 mGal are generally interpreted as accreted/subducting relief in the form of seamounts and other bathymetric features. While most of these anomalies, which have radii < 50km, are correlated with areas of reduced seismicity, several in regions such as Japan and Java appear to have influenced the nucleation and/or propagation of large magnitude earthquakes. Long-wavelength (500 - >1000 km) trench-parallel forearc ridges with residual anomalies of up to 1.5 km and 150 mGal are identified in approximately one-third of the subduction zones analyzed. Despite great length along strike, these ridges are less than 100 km wide and several appear uncompensated. A high proportion of arc-normal structure and the truncation/morphological transition of trench-parallel forearc ridges is explained through the identification and tracking of pre-existing structure on the over-riding and subducting plates into the seismogenic portion of the plate boundary. Spatial correlations between regions with well-defined trench-parallel forearc ridges and the occurrence of large magnitude interplate earthquakes, in addition to the uncompensated state of these ridges, suggest links

  16. Improving the geological interpretation of magnetic and gravity satellite anomalies

    NASA Technical Reports Server (NTRS)

    Hinze, William J.; Braile, Lawrence W.; Vonfrese, Ralph R. B.

    1987-01-01

    Quantitative analysis of the geologic component of observed satellite magnetic and gravity fields requires accurate isolation of the geologic component of the observations, theoretically sound and viable inversion techniques, and integration of collateral, constraining geologic and geophysical data. A number of significant contributions were made which make quantitative analysis more accurate. These include procedures for: screening and processing orbital data for lithospheric signals based on signal repeatability and wavelength analysis; producing accurate gridded anomaly values at constant elevations from the orbital data by three-dimensional least squares collocation; increasing the stability of equivalent point source inversion and criteria for the selection of the optimum damping parameter; enhancing inversion techniques through an iterative procedure based on the superposition theorem of potential fields; and modeling efficiently regional-scale lithospheric sources of satellite magnetic anomalies. In addition, these techniques were utilized to investigate regional anomaly sources of North and South America and India and to provide constraints to continental reconstruction. Since the inception of this research study, eleven papers were presented with associated published abstracts, three theses were completed, four papers were published or accepted for publication, and an additional manuscript was submitted for publication.

  17. Local Earth's gravity field in view of fractal dimension

    NASA Astrophysics Data System (ADS)

    Mészárosová, Katarína; Minarechová, Zuzana; Janák, Juraj

    2013-04-01

    The poster presents the relative roughness of chosen characteristics of the Earth's gravity field in several small regions in area of Slovakia (e.g. free-air anomaly, Bouguer anomaly, gravity disturbance...) using the values of fractal dimension. In this approach, a three dimensional box counting method and the Hurst analysis method are applied to estimate the values of fractal dimensions. Then the computed fractal dimension values are used to compare all 3D models of all chosen characteristics.

  18. A priori noise and regularization in least squares collocation of gravity anomalies

    NASA Astrophysics Data System (ADS)

    Jarmołowski, Wojciech

    2013-12-01

    The paper describes the estimation of covariance parameters in least squares collocation (LSC) by the cross-validation (CV) technique called leave-one-out (LOO). Two parameters of Gauss-Markov third order model (GM3) are estimated together with a priori noise standard deviation, which contributes significantly to the covariance matrix composed of the signal and noise. Numerical tests are performed using large set of Bouguer gravity anomalies located in the central part of the U.S. Around 103 000 gravity stations are available in the selected area. This dataset, together with regular grids generated from EGM2008 geopotential model, give an opportunity to work with various spatial resolutions of the data and heterogeneous variances of the signal and noise. This plays a crucial role in the numerical investigations, because the spatial resolution of the gravity data determines the number of gravity details that we may observe and model. This establishes a relation between the spatial resolution of the data and the resolution of the gravity field model. This relation is inspected in the article and compared to the regularization problem occurring frequently in data modeling. Artykuł opisuje estymację parametrów kowariancji w kolokacji najmniejszych kwadratów (LSC) przy pomocy techniki kroswalidacji nazywanej leave-one-out (LOO). Wyznaczane są dwa parametry modelu Gaussa-Markova trzeciego rzędu (GM3) wraz z odchyleniem standardowym szumu a priori, które ma znaczny wpływ na macierz kowariancji złożoną z sygnału i szumu. Testy numeryczne przeprowadzono na dużym zbiorze anomalii grawimetrycznych Bouguera z obszaru centralnej części USA. Obszar ten mieści około 103000 pomiarów grawimetrycznych. Dane te wraz z regularnymi siatkami wygenerowanymi z modelu geopotencjalnego EGM2008 pozwalają na pracę z różną rozdzielczością przestrzenną i różnymi wariancjami sygnału i szumu. Odgrywa to kluczową rolę w badaniach numerycznych, ponieważ rozdzielczo

  19. Gravity anomalies of the active mud diapirs off southwest Taiwan

    NASA Astrophysics Data System (ADS)

    Doo, Wen-Bin; Hsu, Shu-Kun; Lo, Chung-Liang; Chen, Song-Chuen; Tsai, Ching-Hui; Lin, Jing-Yi; Huang, Yuan-Ping; Huang, Yin-Sheng; Chiu, Shye-Donq; Ma, Yu-Fang

    2015-12-01

    Overpressure and buoyant effect of underlying sediments are generally used to account for the upward motion or formation of submarine mud volcanoes and mud diapirs. In this study, we process and interpret the gravity anomalies associated with the active mud diapirs off SW Taiwan. Geologically, the mud diapirs are just formed and are still very active, thus we can better understand the initial process of the mud diapirs formation through the gravity analysis. Our results show that the density contrasts of the submarine mud diapirs with respect to the surroundings are generally positive. Because the study area is in a tectonically compressive regime and the gas plume venting from the submarine mud volcanoes is very active, we thus infer that mechanically the mud diapirs off SW Taiwan have been formed mainly due to the tectonic compression on the underlying sediments of high pore-fluid pressure, instead of the buoyancy of the buried sediments. The overpressured sediments and fluid are compressed and pushed upwards to pierce the overlying sediments and form the more compacted mud diapirs. The relatively denser material of the mud diapirs probably constrains the flowing courses of the submarine canyons off SW Taiwan, especially for the upper reaches of the Kaoping and Fangliao submarine canyons.

  20. Global correlation of topographic heights and gravity anomalies

    NASA Technical Reports Server (NTRS)

    Roufosse, M. C.

    1977-01-01

    The short wavelength features were obtained by subtracting a calculated 24th-degree-and-order field from observed data written in 1 deg x 1 deg squares. The correlation between the two residual fields was examined by a program of linear regression. When run on a worldwide scale over oceans and continents separately, the program did not exhibit any correlation; this can be explained by the fact that the worldwide autocorrelation function for residual gravity anomalies falls off much faster as a function of distance than does that for residual topographic heights. The situation was different when the program was used in restricted areas, of the order of 5 deg x 5 deg square. For 30% of the world,fair-to-good correlations were observed, mostly over continents. The slopes of the regression lines are proportional to apparent densities, which offer a large spectrum of values that are being interpreted in terms of features in the upper mantle consistent with available heat-flow, gravity, and seismic data.

  1. Gravity anomalies, caldera structure, and subsurface geology in the Rotorua area, New Zealand

    SciTech Connect

    Hunt, T.M. )

    1992-04-01

    This paper discusses a re-examination of gravity which indicates that Rotorua Caldera does not have the circular, negative gravity anomaly typical of other rhyolitic calderas. New gravity measurements and residual gravity anomalies in Rotorua City are consistent with numerous rhyolite domes and ignimbrite sheets, interbedded with a thick sequence of poorly-compacted sediments. Within the city a gravity high extends from the shore of Lake Rotorua south to Whakarewarewa and is associated with a buried ridge, formed by the coalescing of two rhyolite domes. A gravity low centered near Linton Park suggests that rhyolites are thin or absent in this area and sediments extend to a depth of about 1 km. A quantitative analysis of the residual gravity anomalies was limited by insufficient information about the density, extent, and thickness of the material underlying the rhyolites, and the uncertainty in the distribution and density of silicification within the sediments.

  2. Gravity Anomalies in the Northern Hawaiian Islands: Evidence for an Alternative Magma Chamber on Kauai and a Conjoined Niihau-Kauai Island

    NASA Astrophysics Data System (ADS)

    Flinders, A. F.; Ito, G.; Garcia, M.; Kim, S.; Appelgate, B.

    2008-12-01

    The shield stage evolution of the islands of Kauai and Niihau are poorly understood. Previous land-based gravity surveys provide only a coarse constraint on the observed gravitational field. Questions as to whether the island of Kauai was formed by a single or multiple shields and the developmental relationship between these neighboring islands are still debated. Our new land-based gravity survey of Kauai and ship-board gravity surveys around both islands identified large complete Bouguer gravitational anomalies under Kauai's Lihue Basin and offshore in the Kaulakahi Channel, a 30-km-long bathymetric ridge connecting the two islands. These gravitational highs are consistent in size and magnitude with those of other Hawaiian islands and imply local zones of high density crust, most likely attributed to magmatic intrusions; e.g. former magma chambers, or rift zones. The Lihue Basin anomaly observed is offset 20 km east from the geologically mapped caldera region. This offset implies either the unlikely case that the shield stage plumbing system connecting the magma chamber and caldera could have been inclined by up to 75 degrees from the vertical, or that the currently mapped caldera is a late feature, unrelated to shield volcanism. The location of the gravitational anomaly, in the Kaulakahi Channel, 20 km east of Niihau is consistent with geologic mapping, which indicates that Niihau is a remnant of an ancient shield volcano centered east of the island. The proximity of the Niihau gravitational anomaly 10 km from the western edge of Kauai supports the hypothesis that the two volcanoes were part of the same island.

  3. The quest for the perfect gravity anomaly: Part 1 - New calculation standards

    USGS Publications Warehouse

    Li, X.; Hildenbrand, T.G.; Hinze, W. J.; Keller, Gordon R.; Ravat, D.; Webring, M.

    2006-01-01

    The North American gravity database together with databases from Canada, Mexico, and the United States are being revised to improve their coverage, versatility, and accuracy. An important part of this effort is revision of procedures and standards for calculating gravity anomalies taking into account our enhanced computational power, modern satellite-based positioning technology, improved terrain databases, and increased interest in more accurately defining different anomaly components. The most striking revision is the use of one single internationally accepted reference ellipsoid for the horizontal and vertical datums of gravity stations as well as for the computation of the theoretical gravity. The new standards hardly impact the interpretation of local anomalies, but do improve regional anomalies. Most importantly, such new standards can be consistently applied to gravity database compilations of nations, continents, and even the entire world. ?? 2005 Society of Exploration Geophysicists.

  4. An Anzatz about Gravity, Cosmology, and the Pioneer Anomaly

    SciTech Connect

    Murad, Paul

    2010-01-28

    The Pulsar 1913+16 binary system may represent a 'young' binary system where previously it is claimed that the dynamics are due to either a third body or a gravitational vortex. Usually a binary system's trajectory could reside in a single ellipse or circular orbit; the double ellipse implies that the 1913+16 system may be starting to degenerate into a single elliptical trajectory. This could be validated only after a considerably long time period. In a majority of binary star systems, the weights of both stars are claimed by analysis to be the same. It may be feasible that the trajectory of the primary spinning star could demonstrate repulsive gravitational effects where the neutron star's high spin rate induces a repulsive gravitational source term that compensates for inertia. If true, then it provides evidence that angular momentum may be translated into linear momentum as a repulsive source that has propulsion implications. This also suggests mass differences may dictate the neutron star's spin rate as an artifact of a natural gravitational process. Moreover, the reduced matter required by the 'dark' mass hypothesis may not exist but these effects could be due to repulsive gravity residing in rotating celestial bodies.The Pioneer anomaly observed on five different deep-space spacecraft, is the appearance of a constant gravitational force directed toward the sun. Pioneer spacecraft data reveals that a vortex-like magnetic field exists emanating from the sun. The spiral arms of the Sun's magnetic vortex field may be causal to this constant acceleration. This may profoundly provide a possible experimental verification on a cosmic scale of Gertsenshtein's principle relating gravity to electromagnetism. Furthermore, the anomalous acceleration may disappear once the spacecraft passes out into a magnetic spiral furrow, which is something that needs to be observed in the future. Other effects offer an explanation from space-time geometry to the Yarkovsky thermal

  5. High-resolution airborne gravity imaging over James Ross Island (West Antarctica)

    USGS Publications Warehouse

    Jordan, T.A.; Ferraccioli, F.; Jones, P.C.; Smellie, J.L.; Ghidella, M.; Corr, H. F. J.; Zakrajsek, A.F.

    2007-01-01

    James Ross Island (JRI) exposes a Miocene-Recent alkaline basaltic volcanic complex that developed in a back-arc, east of the northern Antarctic Peninsula. JRI has been the focus of several geological studies because it provides a window on Neogene magmatic processes and paleoenvironments. However, little is known about its internal structure. New airborne gravity data were collected as part of the first high-resolution aerogeophysical survey flown over the island and reveal a prominent negative Bouguer gravity anomaly over Mt Haddington. This is intriguing as basaltic volcanoes are typically associated with positive Bouguer anomalies, linked to underlying mafic intrusions. The negative Bouguer anomaly may be associated with a hitherto unrecognised low-density sub-surface body, such as a breccia-filled caldera, or a partially molten magma chamber.

  6. Crustal structure and gravity anomalies beneath the Rif, northern Morocco: implications for the current tectonics of the Alboran region

    NASA Astrophysics Data System (ADS)

    Petit, Carole; Le Pourhiet, Laetitia; Scalabrino, Bruno; Corsini, Michel; Bonnin, Mickaël; Romagny, Adrien

    2015-07-01

    We analyse Bouguer anomaly data and previously published Moho depths estimated from receiver functions in order to determine the amount of isostatic compensation or uncompensation of the Rif topography in northern Morocco. We use Moho depth variations extracted from receiver function analyses to predict synthetic Bouguer anomalies that are then compared to observed Bouguer anomaly. We find that Moho depth variations due to isostatic compensation of topographic and/or intracrustal loads do not match Moho depth estimates obtained from receiver function analyses. The isostatic misfit map evidences excess crustal root as large as 10 km in the western part of the study area, whereas a `missing' crustal root of ˜5 km appears east of 4.3°E. This excess root/missing topography correlates with the presence of a dense mantle lid, the noticeable southwestward drift of the Western Rif area, and with a current surface uplift. We propose that a delaminated mantle lid progressively detaching westward or southwestward from the overlying crust is responsible for viscous flow of the ductile lower crust beneath the Rif area. This gives rise to isostatic uplift and westward drift due to viscous coupling at the upper/lower crust boundary. At the same time, the presence of this dense sinking mantle lid causes a negative dynamic topography, which explains why the observed topography is too low compared to the crustal thickness.

  7. Procedures and results related to the direct determination of gravity anomalies from satellite and terrestrial gravity data

    NASA Technical Reports Server (NTRS)

    Rapp, R. H.

    1974-01-01

    The equations needed for the incorporation of gravity anomalies as unknown parameters in an orbit determination program are described. These equations were implemented in the Geodyn computer program which was used to process optical satellite observations. The arc dependent parameter unknowns, 184 unknown 15 deg and coordinates of 7 tracking stations were considered. Up to 39 arcs (5 to 7 days) involving 10 different satellites, were processed. An anomaly solution from the satellite data and a combination solution with 15 deg terrestrial anomalies were made. The limited data samples indicate that the method works. The 15 deg anomalies from various solutions and the potential coefficients implied by the different solutions are reported.

  8. Classical geometrical interpretation of ghost fields and anomalies in Yang-Mills theory and quantum gravity

    SciTech Connect

    Thierry-Mieg, J.

    1985-05-14

    The reinterpretation of the BRS equations of Quantum Field Theory as the Maurer Cartan equation of a classical principal fiber bundle leads to a simple gauge invariant classification of the anomalies in Yang Mills theory and gravity.

  9. On the ratio of dynamic topography and gravity anomalies in a dynamic Earth

    NASA Astrophysics Data System (ADS)

    Colli, L.; Ghelichkhan, S.; Bunge, H.-P.

    2016-03-01

    Growing evidence from a variety of geologic indicators points to significant topography maintained convectively by viscous stresses in the mantle. However, while gravity is sensitive to dynamically supported topography, there are only small free-air gravity anomalies (<30 mGal) associated with Earth's long-wavelength topography. This has been used to suggest that surface heights computed assuming a complete isostatic equilibrium provide a good approximation to observed topography. Here we show that the apparent paradox is resolved by the well-established formalism of global, self-gravitating, viscously stratified Earth models. The models predict a complex relation between dynamic topography, mass, and gravity anomalies that is not summarized by a constant admittance—i.e., ratio of gravity anomalies to surface deflections—as one would infer from analytic flow solutions formulated in a half-space. Our results suggest that sizable dynamic topography may exist without a corresponding gravity signal.

  10. Analysis of gravity anomaly over coral-reef oil field: Wilfred Pool, Sullivan County, Indiana

    SciTech Connect

    Dana, S.W.

    1980-03-01

    To compare the measured and theoretical gravity anomaly of a typical coral-reef oil field, data were collected from the wilfred Pool, Sullivan County, Indiana. Densities of available core samples from the field were determined and the anomaly was calculated, taking into account the lateral and vertical variation of density and the geologic structure known from core studies and drilling-log records of lithologic types penetrated by the wells. Comparison of the theoretical and actual anomalies indicated a rough correspondence except for several sharp negative anomalies on the flanks of the measured gravity anomaly. Further studies indicated that the negative anomalies are possibly due to fluvial erosion that produced, on the surface of the youngest Pennsylvanian sediments, channels which were later filled with glacial till of lower density than the sediments. 13 figures.

  11. Gravity anomalies, plate tectonics and the lateral growth of Precambrian North America

    NASA Technical Reports Server (NTRS)

    Thomas, M. D.; Grieve, R. A. F.; Sharpton, V. L.

    1988-01-01

    The widespread gravity coverage of North America provides a picture of the gross structural fabric of the continent via the trends of gravity anomalies. The structural picture so obtained reveals a mosaic of gravity trend domains, many of which correlate closely with structural provinces and orogenic terranes. The gravity trend map, interpreted in the light of plate-tectonic theory, thus provides a new perspective for examining the mode of assembly and growth of North America. Suture zones, palaeosubduction directions, and perhaps, contrasting tectonic histories may be identified using gravity patterns.

  12. Gravity data from the San Pedro River Basin, Cochise County, Arizona

    USGS Publications Warehouse

    Kennedy, Jeffrey R.; Winester, Daniel

    2011-01-01

    The U.S. Geological Survey, Arizona Water Science Center in cooperation with the National Oceanic and Atmospheric Administration, National Geodetic Survey has collected relative and absolute gravity data at 321 stations in the San Pedro River Basin of southeastern Arizona since 2000. Data are of three types: observed gravity values and associated free-air, simple Bouguer, and complete Bouguer anomaly values, useful for subsurface-density modeling; high-precision relative-gravity surveys repeated over time, useful for aquifer-storage-change monitoring; and absolute-gravity values, useful as base stations for relative-gravity surveys and for monitoring gravity change over time. The data are compiled, without interpretation, in three spreadsheet files. Gravity values, GPS locations, and driving directions for absolute-gravity base stations are presented as National Geodetic Survey site descriptions.

  13. Lithologic mapping test for gravity and magnetic anomalies. A case study of gravity-magnetic anomaly profile in the eastern segment of the China-Mongolia border

    NASA Astrophysics Data System (ADS)

    Wang, Jian; Meng, Xiaohong; Chen, Zhaoxi; Liu, Guofeng; Zheng, Yuanman; Wang, Jun; Zhang, Sheng; Zhang, Xingdong; Zheng, Wanqiu

    2015-06-01

    An inversion calculation is usually needed to map lithologies with gravity-magnetic anomalies. A lithological-physical property correspondence can be established by combining data of regional rock density and magnetic susceptibility to build topological equations. In this study, topological calculations were performed using inversion data and combined with physical property data to interpret and map lithologies. Gravity-magnetic profiles from the eastern segment of the China-Mongolia border were used (Jining-Bainaimiao-Ha'ernaode geological-composite geophysical profile) in this paper. Based on gravity-magnetic anomaly inversion, the rock density and magnetic susceptibility data of Bainaimiao and Jining were adopted for lithological inversion. Distribution characteristics of four major types of magmatic rocks within 50 km of the lower half space were obtained, and results of lithologic mapping and tectonic framework were analyzed. The position of convergence between the North China Plate and Siberian Plate was confirmed. Two tectonic stages were identified, namely, interplate squeezing and intraplate deformation. Regional gravity-magnetic field properties were analyzed to discuss the orientation and date of andesites and diorites in the northern part of the survey line. We believe that they have a northeast-southwest orientation similar to gravity-magnetic anomalies of Erenhot-Xilinhot. They resemble the igneous rock near Erenhot because they both indicate magmatic intrusion during the early Carboniferous.

  14. Improving the geological interpretation of magnetic and gravity satellite anomalies

    NASA Technical Reports Server (NTRS)

    Hinze, W. J.; Braile, L. W. (Principal Investigator); Vonfrese, R. R. B.

    1985-01-01

    Current limitations in the quantitative interpretation of satellite-elevation geopotential field data and magnetic anomaly data were investigated along with techniques to overcome them. A major result was the preparation of an improved scalar magnetic anomaly map of South America and adjacent marine areas directly from the original MAGSAT data. In addition, comparisons of South American and Euro-African data show a strong correlation of anomalies along the Atlantic rifted margins of the continents.

  15. Lithospheric structure across the central Tien Shan constrained by gravity anomalies and joint inversions of receiver function and Rayleigh wave dispersion

    NASA Astrophysics Data System (ADS)

    Li, Yonghua; Shi, Lei; Gao, Jiayi

    2016-07-01

    Shear wave velocity structure across the central Tien Shan orogeny was generated by jointly inverting Rayleigh wave phase and group velocity with teleseismic P-wave receiver functions at 40 broadband seismic stations. The inferred seismic structure was validated by forward modeling of the complete Bouguer anomaly data. The joint inversion result reveals larger crust thicknesses beneath the Kokshaal (∼68-72 km) and Kyrgyz ranges (∼62-64 km), while other units have crustal thicknesses between 48 and 58 km. A fast velocity layer (Vs = 3.6-3.9 km/s) in the upper crust is found in some seismic stations within the Kazakh Shield. Our models show the presence of high velocity and density layers in the lowermost crust throughout the region, consistent with the presence of mafic/ultramafic lithologies. The large crustal thickness is associated with a thickened mafic layer in the lower crust, indicating that the thickened crust may be partly caused by magmatic underplating. The low velocity and density anomaly in the middle crust, and low upper mantle velocity observed in our model beneath the middle Tien Shan reflect the presence of partial melt in the crust due to the intrusion of hot mantle material. The lack of correlation between Moho depth and topography, together with the gravity results, suggests that the topographic compensation in the central Tien Shan is not confined to the crust. This requires significant support from the mantle to account for the relative high elevation of the middle Tien Shan.

  16. Inversion of Oceanic Lithosphere Density Structure in the South China Sea by Satellite Gravity

    NASA Astrophysics Data System (ADS)

    Zhang, S.

    2013-12-01

    In this paper, the satellite altimetry gravity anomaly is used to calculate the Bouguer gravity by Seafloor terrain correction in the South China Sea. The faults distribution and basin boundary is extracted to study the geological structure unit. The 3D density inversion method is applied to invert the oceanic lithosphere density structure. In the 3D density inversion method, the depth weighting function is an experience function derived by the relation between gravity anomaly and depth. It is difficult to artificially choose reasonable values of the weighting factors which have great effect on the inversion result. The power spectrum of the gravity anomaly is used to estimate the depth of the geological body, and the function of the weighting factors and the gravity anomaly is built. The weighting factors can be estimated automatically by the gravity anomaly power spectrum. Therefore, the artificial error can be avoided and the accuracy of inversion is improved. In the density inversion, the Bouguer gravity is firstly decomposed into different scales by wavelet transform method. The gravity anomaly in different scales is related to the density distribution in different depth. Then, the power spectrum is calculated by gravity anomaly in different scales to estimate the weighting factors. Finally, the ocean lithosphere density structure in the South China Sea is inverted and compared with its velocity structure.

  17. Relation of the lunar volcano complexes lying on the identical linear gravity anomaly

    NASA Astrophysics Data System (ADS)

    Yamamoto, K.; Haruyama, J.; Ohtake, M.; Iwata, T.; Ishihara, Y.

    2015-12-01

    There are several large-scale volcanic complexes, e.g., Marius Hills, Aristarchus Plateau, Rumker Hills, and Flamsteed area in western Oceanus Procellarum of the lunar nearside. For better understanding of the lunar thermal history, it is important to study these areas intensively. The magmatisms and volcanic eruption mechanisms of these volcanic complexes have been discussed from geophysical and geochemical perspectives using data sets acquired by lunar explorers. In these data sets, precise gravity field data obtained by Gravity Recovery and Interior Laboratory (GRAIL) gives information on mass anomalies below the lunar surface, and useful to estimate location and mass of the embedded magmas. Using GRAIL data, Andrews-Hanna et al. (2014) prepared gravity gradient map of the Moon. They discussed the origin of the quasi-rectangular pattern of narrow linear gravity gradient anomalies located along the border of Oceanus Procellarum and suggested that the underlying dikes played important roles in magma plumbing system. In the gravity gradient map, we found that there are also several small linear gravity gradient anomaly patterns in the inside of the large quasi-rectangular pattern, and that one of the linear anomalies runs through multiple gravity anomalies in the vicinity of Aristarchus, Marius and Flamstead volcano complexes. Our concern is whether the volcanisms of these complexes are caused by common factors or not. To clarify this, we firstly estimated the mass and depth of the embedded magmas as well as the directions of the linear gravity anomalies. The results were interpreted by comparing with the chronological and KREEP distribution maps on the lunar surface. We suggested providing mechanisms of the magma to these regions and finally discussed whether the volcanisms of these multiple volcano complex regions are related with each other or not.

  18. Long-wavelength Magnetic and Gravity Anomaly Correlations of Africa and Europe

    NASA Technical Reports Server (NTRS)

    Vonfrese, R. R. B.; Hinze, W. J. (Principal Investigator); Olivier, R.

    1984-01-01

    Preliminary MAGSAT scalar magnetic anomaly data were compiled for comparison with long-wavelength-pass filtered free-air gravity anomalies and regional heat-flow and tectonic data. To facilitate the correlation analysis at satellite elevations over a spherical-Earth, equivalent point source inversion was used to differentially reduce the magnetic satellite anomalies to the radial pole at 350 km elevation, and to upward continue the first radial derivative of the free-air gravity anomalies. Correlation patterns between these regional geopotential anomaly fields are quantitatively established by moving window linear regression based on Poisson's theorem. Prominent correlations include direct correspondences for the Baltic Shield, where both anomalies are negative, and the central Mediterranean and Zaire Basin where both anomalies are positive. Inverse relationships are generally common over the Precambrian Shield in northwest Africa, the Basins and Shields in southern Africa, and the Alpine Orogenic Belt. Inverse correlations also presist over the North Sea Rifts, the Benue Rift, and more generally over the East African Rifts. The results of this quantitative correlation analysis support the general inverse relationships of gravity and magnetic anomalies observed for North American continental terrain which may be broadly related to magnetic crustal thickness variations.

  19. Long-wavelength magnetic and gravity anomaly correlations on Africa and Europe

    NASA Technical Reports Server (NTRS)

    Vonfrese, R. R. B.; Olivier, R.; Hinze, W. J.

    1985-01-01

    Preliminary MAGSAT scalar magnetic anomaly data were compiled for comparison with long-wavelength-pass filtered free-air gravity anomalies and regional heat-flow and tectonic data. To facilitate the correlation analysis at satellite elevations over a spherical-Earth, equivalent point source inversion was used to differentially reduce the magnetic satellite anomalies to the radial pole at 350 km elevation, and to upward continue the first radial derivative of the free-air gravity anomalies. Correlation patterns between these regional geopotential anomaly fields are quantitatively established by moving window linear regression based on Poisson's theorem. Prominent correlations include direct correspondences for the Baltic shield, where both anomalies are negative, and the central Mediterranean and Zaire Basin where both anomalies are positive. Inverse relationships are generally common over the Precambrian Shield in northwest Africa, the Basins and Shields in southern Africa, and the Alpine Orogenic Belt. Inverse correlations also presist over the North Sea Rifts, the Benue Rift, and more generally over the East African Rifts. The results of this quantitative correlation analysis support the general inverse relationships of gravity and magnetic anomalies observed for North American continental terrain which may be broadly related to magnetic crustal thickness variations.

  20. Global accuracy estimates of point and mean undulation differences obtained from gravity disturbances, gravity anomalies and potential coefficients

    NASA Technical Reports Server (NTRS)

    Jekeli, C.

    1979-01-01

    Through the method of truncation functions, the oceanic geoid undulation is divided into two constituents: an inner zone contribution expressed as an integral of surface gravity disturbances over a spherical cap; and an outer zone contribution derived from a finite set of potential harmonic coefficients. Global, average error estimates are formulated for undulation differences, thereby providing accuracies for a relative geoid. The error analysis focuses on the outer zone contribution for which the potential coefficient errors are modeled. The method of computing undulations based on gravity disturbance data for the inner zone is compared to the similar, conventional method which presupposes gravity anomaly data within this zone.

  1. GEOS 3 data processing for the recovery of geoid undulations and gravity anomalies

    NASA Technical Reports Server (NTRS)

    Rapp, R. H.

    1979-01-01

    The paper discusses the analysis of GEOS 3 altimeter data for the determination of geoid heights and point and mean gravity anomalies. Methods are presented for determining the mean anomalies and mean undulations from the GEOS 3 altimeter data available by the end of September 1977 without having a complete set of precise orbits. The editing of the data is extensive to remove questionable data, although no filtering of the data is carried out. An adjustment process is carried out to eliminate orbit error and altimeter bias. Representative point anomaly values are computed to investigate anomaly behavior across the Bonin Trench and over the Patton seamounts.

  2. Mantle origin of the Emeishan large igneous province from an analysis of residual gravity anomalies

    NASA Astrophysics Data System (ADS)

    Deng, Y.; Zhang, Z.; Mooney, W. D.; Fan, W.; Zhong, Q.; Badal, J.

    2013-12-01

    The Emeishan large igneous province (ELIP) is the only verified large igneous province in China. It covers an area of 250,000 km2 from the eastern margin of the Tibetan Plateau to the western margin of the Yangtze block. Most studies on ELIP are from geochemistry and tectonics, but the deep origin of the ELIP is still unclear. In this study, we investigate the residual gravity anomaly in South China and its relationship to the Emeishan large igneous province with constrains of lithospheric structure from deep seismic sounding profiles, deep seismic reflection surveys, and a variety of broadband seismic observations acquired in South China in the last several decades. Our working scheme consists of removing the respective gravitational effects due to: (1) the sediments, and undulations of the (2) crystalline basement, (3) upper crust; (4) Moho and (5) lithospheric thickness. We have thus obtained the residual gravity anomaly of the ELIP and surrounding region, striking positive residual anomaly with maximum value of 140 mGal is observed at the ELIP region. We use the conjugate gradient method to locate the deep origins of the residual gravity data. As a result, our preferred model consists of a positive cylindrical density anomaly that provides a fit to the residual gravity anomaly observed in ELIP. As the distance increases from the inner zone of the ELIP to the outer zone, the positive residual gravity decreases. Hence, in our model, the density anomaly decreases from about 0.06 g/cm3 beneath the inner zone to about 0.03 g/cm3 beneath the outer zone. The residual gravity and our preferred density anomaly provide new evidence, along with the seismic data and geochemical data, to confirm the domal structure of the Permian mantle plume that gave rise to the Emenshan Large Igneous Province.

  3. Interpretations of gravity and magnetic anomalies in the Songliao Basin with Wavelet Multi-scale Decomposition

    NASA Astrophysics Data System (ADS)

    Li, Changbo; Wang, Liangshu; Sun, Bin; Feng, Runhai; Wu, Yongjing

    2015-09-01

    In this paper, we introduce the method of Wavelet Multi-scale Decomposition (WMD) combined with Power Spectrum Analysis (PSA) for the separation of regional gravity and magnetic anomalies. The Songliao Basin is situated between the Siberian Plate and the North China Plate, and its main structural trend of gravity and magnetic anomaly fields is NNE. The study area shows a significant feature of deep collage-type construction. According to the feature of gravity field, the region was divided into five sub-regions. The gravity and magnetic fields of the Songliao Basin were separated using WMD with a 4th order separation. The apparent depth of anomalies in each order was determined by Logarithmic PSA. Then, the shallow high-frequency anomalies were removed and the 2nd-4th order wavelet detail anomalies were used to study the basin's major faults. Twenty-six faults within the basement were recognized. The 4th order wavelet approximate anomalies were used for the inversion of the Moho discontinuity and the Curie isothermal surface.

  4. Investigation of urban faults in Shenzhen using wavelet multi-scale analysis and modeling of gravity observations

    NASA Astrophysics Data System (ADS)

    Xu, Chuang; Chen, Liang; Liu, Xi-kai

    2016-04-01

    Urban faults in Shenzhen are potential threat to the city security and sustainable development. To improve the knowledge of the Shenzhen fault zone, interpretation and inversion of gravity data were carried out. Bouguer gravity covering the whole Shenzhen city was calculated with a resolution of 1kmx1km. Wavelet multi-scale analysis (MSA) was applied to the Bouguer gravity data to obtain the multilayer residual anomalies corresponding to different depths. In addition, 2D gravity models were constructed along three profiles. The Bouguer gravity anomaly shows a NE-striking high-low-high pattern from northwest to southeast, strongly related to the main faults. According to the result of MSA, the correlation between gravity anomaly and faults is particularly significant from 4 to 12 km depth. The residual gravity with small amplitude in each layer indicates weak tectonic activity in the crust. In the upper layers, positive anomalies along most of faults reveal the upwelling of high-density materials during the past tectonic movements. The multilayer residual anomalies also implicate important information about the faults, such as the vertical extension and the dip direction. The maximum depth of the faults is about 20km. In general, NE-striking faults extend deeper than NW-striking Faults and have a larger dip angle. This study is supported by the National Natural Science Foundation of China (Grant No.41504015) and China Postdoctoral Science Foundation (Grant No.2015M572146).

  5. South China Sea crustal thickness and lithosphere thinning from satellite gravity inversion incorporating a lithospheric thermal gravity anomaly correction

    NASA Astrophysics Data System (ADS)

    Kusznir, Nick; Gozzard, Simon; Alvey, Andy

    2016-04-01

    The distribution of ocean crust and lithosphere within the South China Sea (SCS) are controversial. Sea-floor spreading re-orientation and ridge jumps during the Oligocene-Miocene formation of the South China Sea led to the present complex distribution of oceanic crust, thinned continental crust, micro-continents and volcanic ridges. We determine Moho depth, crustal thickness and continental lithosphere thinning (1- 1/beta) for the South China Sea using a gravity inversion method which incorporates a lithosphere thermal gravity anomaly correction (Chappell & Kusznir, 2008). The gravity inversion method provides a prediction of ocean-continent transition structure and continent-ocean boundary location which is independent of ocean isochron information. A correction is required for the lithosphere thermal gravity anomaly in order to determine Moho depth accurately from gravity inversion; the elevated lithosphere geotherm of the young oceanic and rifted continental margin lithosphere of the South China Sea produces a large lithosphere thermal gravity anomaly which in places exceeds -150 mGal. The gravity anomaly inversion is carried out in the 3D spectral domain (using Parker 1972) to determine 3D Moho geometry and invokes Smith's uniqueness theorem. The gravity anomaly contribution from sediments assumes a compaction controlled sediment density increase with depth. The gravity inversion includes a parameterization of the decompression melting model of White & McKenzie (1999) to predict volcanic addition generated during continental breakup lithosphere thinning and seafloor spreading. Public domain free air gravity anomaly, bathymetry and sediment thickness data are used in this gravity inversion. Using crustal thickness and continental lithosphere thinning factor maps with superimposed shaded-relief free-air gravity anomaly, we improve the determination of pre-breakup rifted margin conjugacy, rift orientation and sea-floor spreading trajectory. SCS conjugate margins

  6. Detailed Gravity and Magnetic Survey of the Taylorsville Triassic Basin

    SciTech Connect

    Leftwich, John; Nowroozi, Ali, A.

    1999-10-01

    This work reports the progress on collecting existing gravity data in a rectangular area covering the Richmond and Taylorsville Basins and its vicinity. The area covers one-degree latitude and one degree longitude, starting at 37 North, 77 West and ending at 38 North, 78 West. Dr. David Daniels of the United State Geological Survey supplied us with more than 4900 Bouguer gravity anomalies in this area. The purpose of this report is to present the data in form of several maps and discuss its relation to the geology of the Triassic Basins and its vicinity. Johnson and others (1985) also presented a map of the Bouguer gravity anomaly of this area. However, their map covers a smaller area, and it is based on smaller number of observations.

  7. On the recovery of gravity anomalies from high precision altimeter data

    NASA Technical Reports Server (NTRS)

    Lelgemann, D.

    1976-01-01

    A model for the recovery of gravity anomalies from high precision altimeter data is derived which consists of small correction terms to the inverse Stokes' formula. The influence of unknown sea surface topography in the case of meandering currents such as the Gulf Stream is discussed. A formula was derived in order to estimate the accuracy of the gravity anomalies from the known accuracy of the altimeter data. It is shown that for the case of known harmonic coefficients of lower order the range of integration in Stokes inverse formula can be reduced very much.

  8. Gravity anomalies of irregularly shaped two-dimensional bodies with constant horizontal density gradient

    USGS Publications Warehouse

    Pan, Jeng-Jong

    1989-01-01

    An equation to compute the gravity anomalies of two-dimensional (2-D) bodies with density contrast varying with depth (z axis) was developed by Murthy and Rao (1979). I develop an equation for computing the gravity anomalies of 2-D bodies with constant horizontal density gradient. By combining this equation with the equation of Murthy and Rao, I estimate the depth of the sedimentary basin which is adjacent to the master fault associated with the Rio Grande rift in New Mexico, where the density is assumed to decrease basinward from the fault (Cordell, 1979).

  9. Plumes in the mantle. [free air and isostatic gravity anomalies for geophysical interpretation

    NASA Technical Reports Server (NTRS)

    Khan, M. A.

    1973-01-01

    Free air and isostatic gravity anomalies for the purposes of geophysical interpretation are presented. Evidence for the existance of hotspots in the mantle is reviewed. The prosposed locations of these hotspots are not always associated with positive gravity anomalies. Theoretical analysis based on simplified flow models for the plumes indicates that unless the frictional viscosities are several orders of magnitude smaller than the present estimates of mantle viscosity or alternately, the vertical flows are reduced by about two orders of magnitude, the plume flow will generate implausibly high temperatures.

  10. Gravity investigation of the Manson impact structure, Iowa

    NASA Technical Reports Server (NTRS)

    Plescia, J. B.

    1993-01-01

    The Manson crater, of probable Cretaceous/Tertiary age, is located in northwestern Iowa (center at 42 deg. 34.44 min N; 94 deg. 33.60 min W). A seismic reflection profile along an east west line across the crater and drill hole data indicate a crater about 35 km in diameter having the classic form for an impact crater, an uplifted central peak composed of uplifted Proterozoic crystalline bedrock, surrounded by a 'moat' filled with impact produced breccia and a ring graben zone composed of tilted fault blocks of the Proterozoic and Paleozoic country rocks. The structure has been significantly eroded. This geologic structure would be expected to produce a significant gravity signature and study of that signature would shed additional light on the details of the crater structure. A gravity study was undertaken to better resolve the crustal structure. The regional Bouguer gravity field is characterized by a southeastward decreasing field. To first order, the Bouguer gravity field can be understood in the context of the geology of the Precambrian basement. The high gravity at the southeast corner is associated with the mid-continent gravity high; the adjacent low to the northwest results from a basin containing low-density clastic sediments shed from the basement high. Modeling of a simple basin and adjacent high predicts much of the observed Bouguer gravity signature. A gravity signature due to structure associated with the Manson impact is not apparent in the Bouguer data. To resolve the gravity signature of the impact, a series of polynomial surfaces were fit to the Bouguer gravity field to isolate the small wavelength residual anomalies. The residual gravity obtained after subtracting a 5th- or 6th-order polynomial seems to remove most of the regional effects and isolate local anomalies. The pattern resolved in the residual gravity is one of a gravity high surrounded by gravity lows and in turn surrounded by isolated gravity highs. The central portion of the crater

  11. Gravity investigation of the Manson impact structure, Iowa

    NASA Astrophysics Data System (ADS)

    Plescia, J. B.

    1993-03-01

    The Manson crater, of probable Cretaceous/Tertiary age, is located in northwestern Iowa (center at 42 deg. 34.44 min N; 94 deg. 33.60 min W). A seismic reflection profile along an east west line across the crater and drill hole data indicate a crater about 35 km in diameter having the classic form for an impact crater, an uplifted central peak composed of uplifted Proterozoic crystalline bedrock, surrounded by a 'moat' filled with impact produced breccia and a ring graben zone composed of tilted fault blocks of the Proterozoic and Paleozoic country rocks. The structure has been significantly eroded. This geologic structure would be expected to produce a significant gravity signature and study of that signature would shed additional light on the details of the crater structure. A gravity study was undertaken to better resolve the crustal structure. The regional Bouguer gravity field is characterized by a southeastward decreasing field. To first order, the Bouguer gravity field can be understood in the context of the geology of the Precambrian basement. The high gravity at the southeast corner is associated with the mid-continent gravity high; the adjacent low to the northwest results from a basin containing low-density clastic sediments shed from the basement high. Modeling of a simple basin and adjacent high predicts much of the observed Bouguer gravity signature. A gravity signature due to structure associated with the Manson impact is not apparent in the Bouguer data. To resolve the gravity signature of the impact, a series of polynomial surfaces were fit to the Bouguer gravity field to isolate the small wavelength residual anomalies. The residual gravity obtained after subtracting a 5th- or 6th-order polynomial seems to remove most of the regional effects and isolate local anomalies. The pattern resolved in the residual gravity is one of a gravity high surrounded by gravity lows and in turn surrounded by isolated gravity highs. The central portion of the crater

  12. Mafic and ultramafic rocks of the northwestern Brooks Range of Alaska produce nearly symmetric gravity anomalies

    SciTech Connect

    Morin, R.L. )

    1993-04-01

    An arc of mafic and ultramafic rocks is mapped from Asik Mountain to Siniktanneyak Mountain in the northwestern Brooks Range of Alaska. Gravity data, although not very detailed, have been collected over the region and show some very conspicuous circular or oval gravity highs over portions of the mapped mafic-ultramafic bodies. Bodies which have large associated gravity anomalies are Asik Mountain (80 mGal), Avon Hills (20 mGal), Misheguk Mountain (30 mGal), and Siniktanneyak Mountain (20 mGal). Gabbros of the Siniktanneyak Mountain complex, where the gravity coverage is best, have densities of about 3.0 g/cm[sup 3] while the densities of the surrounding sedimentary rocks are about 2.6 g/cm[sup 3]. Volcanic rocks in the area have average densities of about 2.7 g/cm[sup 3]. Three-dimensional modeling indicates that the largest anomaly, on the southwestern part of the complex, could be caused by a polygonal prism of gabbro with vertical sides, about 6 km across and about 4.5 km deep. A smaller lobe of the anomaly on the northeast of the complex could be caused by another oblong polygonal prism about 4 km long and 2 km wide trending northeast and about 1.5 km deep. Modeling this anomaly with densities lower than gabbro would require greater thicknesses to produce the same anomaly. Modeling each anomaly along this arc in 2 1/2-dimensions shows many possible solutions using different body shapes and different density contrasts. There are several other gravity anomalies in this vicinity which could represent unexposed high density rocks. One such anomaly is in the Maiyumerak Mountains northeast of Asik Mountain (30 mGal). Another anomaly is to the northwest of Asik Mountain (20 mGal). There is also an anomaly at Uchugrak (20 mGal) east of Avan Hills. Although many of the anomalies in this region are poorly controlled, an attempt has been made to interpret the data to show possible solutions.

  13. Using Grail Data to Assess the Effect of Porosity and Dilatancy on the Gravity Signature of Impact Craters on the Moon

    NASA Astrophysics Data System (ADS)

    Milbury, C.; Johnson, B. C.; Melosh, J., IV; Collins, G. S.; Blair, D. M.; Soderblom, J. M.; Zuber, M. T.

    2014-12-01

    NASA's dual Gravity Recovery and Interior Laboratory (GRAIL) spacecraft have globally mapped the lunar gravity field at unprecedented resolution; this has enabled the study of craters of all sizes and ages. Soderblom et al. [2014, LPSC abstract #1777] calculated the residual Bouguer anomalies for ~2700 craters 27-184 km in diameter (D). They found that the residual Bouguer anomaly over craters smaller than D~100 km is essentially 0±50 mGal, there is a transition for D~100-150 km, and craters larger than 184 km have a positive residual Bouguer anomaly that increases with increasing crater size. We use the iSALE shock physics hydrocode to model crater formation, including the effect of porosity and dilatancy (shear bulking). We use strength parameters of gabbroic anorthosite for the crust and dunite for the mantle. Our impactor sizes range from 6-30 km, which produce craters between 86-450 km in diameter for pre-impact target porosities of 0, 6.8, and 13.6%. We calculate the free-air and Bouguer gravity anomalies from our models and compare them to gravity data from GRAIL. We find that target porosity has the greatest effect on the gravity signature of lunar craters and can explain the observed ±50 mGal scatter in the residual Bouguer anomaly. We investigate variations of impact velocity, crustal thickness, and dilatancy angle; we find that these parameters do not affect the gravity as significantly as target porosity does. We find that the crater diameter at which mantle uplift dominates the crater gravity is dependent on target porosity, and that it occurs at a crater diameter that is close to the complex crater to peak-ring basin transition.

  14. Kerr metric, geodesic motion, and Flyby Anomaly in fourth-order Conformal Gravity

    NASA Astrophysics Data System (ADS)

    Varieschi, Gabriele U.

    2014-06-01

    In this paper we analyze the Kerr geometry in the context of Conformal Gravity, an alternative theory of gravitation, which is a direct extension of General Relativity (GR). Following previous studies in the literature, we introduce an explicit expression of the Kerr metric in Conformal Gravity, which naturally reduces to the standard GR Kerr geometry in the absence of Conformal Gravity effects. As in the standard case, we show that the Hamilton-Jacobi equation governing geodesic motion in a space-time based on this geometry is indeed separable and that a fourth constant of motion—similar to Carter's constant—can also be introduced in Conformal Gravity. Consequently, we derive the fundamental equations of geodesic motion and show that the problem of solving these equations can be reduced to one of quadratures. In particular, we study the resulting time-like geodesics in Conformal Gravity Kerr geometry by numerically integrating the equations of motion for Earth flyby trajectories of spacecraft. We then compare our results with the existing data of the Flyby Anomaly in order to ascertain whether Conformal Gravity corrections are possibly the origin of this gravitational anomaly. Although Conformal Gravity slightly affects the trajectories of geodesic motion around a rotating spherical object, we show that these corrections are minimal and are not expected to be the origin of the Flyby Anomaly, unless conformal parameters are drastically different from current estimates. Therefore, our results confirm previous analyses, showing that modifications due to Conformal Gravity are not likely to be detected at the Solar System level, but might affect gravity at the galactic or cosmological scale.

  15. Analyzing and modeling gravity and magnetic anomalies using the SPHERE program and Magsat data

    NASA Technical Reports Server (NTRS)

    Braile, L. W.; Hinze, W. J.; Vonfrese, R. R. B. (Principal Investigator)

    1981-01-01

    Computer codes were completed, tested, and documented for analyzing magnetic anomaly vector components by equivalent point dipole inversion. The codes are intended for use in inverting the magnetic anomaly due to a spherical prism in a horizontal geomagnetic field and for recomputing the anomaly in a vertical geomagnetic field. Modeling of potential fields at satellite elevations that are derived from three dimensional sources by program SPHERE was made significantly more efficient by improving the input routines. A preliminary model of the Andean subduction zone was used to compute the anomaly at satellite elevations using both actual geomagnetic parameters and vertical polarization. Program SPHERE is also being used to calculate satellite level magnetic and gravity anomalies from the Amazon River Aulacogen.

  16. Spherical earth gravity and magnetic anomaly analysis by equivalent point source inversion

    NASA Technical Reports Server (NTRS)

    Von Frese, R. R. B.; Hinze, W. J.; Braile, L. W.

    1981-01-01

    To facilitate geologic interpretation of satellite elevation potential field data, analysis techniques are developed and verified in the spherical domain that are commensurate with conventional flat earth methods of potential field interpretation. A powerful approach to the spherical earth problem relates potential field anomalies to a distribution of equivalent point sources by least squares matrix inversion. Linear transformations of the equivalent source field lead to corresponding geoidal anomalies, pseudo-anomalies, vector anomaly components, spatial derivatives, continuations, and differential magnetic pole reductions. A number of examples using 1 deg-averaged surface free-air gravity anomalies of POGO satellite magnetometer data for the United States, Mexico, and Central America illustrate the capabilities of the method.

  17. Gravity and geoid anomalies of the Philippine Sea: Evidence on the depth of compensation for the negative residual water depth anomaly

    NASA Technical Reports Server (NTRS)

    Bowin, C.

    1982-01-01

    A negative free-air gravity anomaly which occurs in the central part of the Philippine Sea was examined to determine the distribution and nature of possible regional mass excesses or deficiencies. Geoid anomalies from GEOS-3 observation were positive. A negative residual geoid anomaly consistent with the area of negative free-air gravity anomalies were found. Theoretical gravity-topography and geoid-topography admittance functions indicated that high density mantle at about 60 km dept could account for the magnitudes of the gravity and residual geoid anomaly and the 1 km residual water depth anomaly in the Philippine Sea. The negative residual depth anomaly may be compensated for by excess density in the uppermost mantle, but the residual geoid and regional free-air gravity anomalies and a slow surface wave velocity structure might result from low-density warm upper mantle material lying beneath the zone of high-density uppermost mantle. From a horizontal disk approximation, the depth of the low-density warm mantle was estimated to be on the order of 200 km.

  18. Gravity anomalies of the Northern Hawaiian Islands: Implications on the shield evolutions of Kauai and Niihau

    NASA Astrophysics Data System (ADS)

    Flinders, Ashton F.; Ito, Garrett; Garcia, Michael O.

    2010-08-01

    New land and marine gravity data reveal two positive residual gravity anomalies in the Northern Hawaiian Islands: one over Kaua'i, the other between the islands of Kaua'i and Ni'ihau. These gravitational highs are similar in size and magnitude to those of other Hawaiian volcanoes, indicating local zones of high-density crust, attributed to olivine cumulates in solidified magma reservoirs. The residual gravity high over Kaua'i is located in the Līhu'e Basin, offset 8-12 km east of Kaua'i's geologically mapped caldera. This offset suggests that the mapped caldera is a collapsed feature later filled in with lava and not the long-term center of Kaua'i shield volcanism. A second residual gravity high, in the submarine channel between Kaua'i and Ni'ihau, marks the volcanic center of the Ni'ihau shield volcano. This second residual gravity anomaly implies that Ni'ihau's eastern boundary extended ˜20 km east of its present location. Through inversion, the residual gravity anomalies were modeled as being produced by two solidified magma reservoirs with average densities of 3100 kg/m3 and volumes between 2470 and 2540 km3. Considering the locations and sizes of the residual gravity anomalies/magma reservoirs, the extent of the two islands' paleoshorelines and potassium-argon dating of shield-stage lavas, we conclude that the two islands were not connected subaerially during their respective shield stages and that Ni'ihau's topographic summit was removed by an eastern flank collapse between 4.3 and 5.6 Ma. Continued constructional volcanism on western Kaua'i likely covered much of the submerged remains of eastern Ni'ihau.

  19. Direct recovery of mean gravity anomalies from satellite to satellite tracking

    NASA Technical Reports Server (NTRS)

    Hajela, D. P.

    1974-01-01

    The direct recovery was investigated of mean gravity anomalies from summed range rate observations, the signal path being ground station to a geosynchronous relay satellite to a close satellite significantly perturbed by the short wave features of the earth's gravitational field. To ensure realistic observations, these were simulated with the nominal orbital elements for the relay satellite corresponding to ATS-6, and for two different close satellites (one at about 250 km height, and the other at about 900 km height) corresponding to the nominal values for GEOS-C. The earth's gravitational field was represented by a reference set of potential coefficients up to degree and order 12, considered as known values, and by residual gravity anomalies obtained by subtracting the anomalies, implied by the potential coefficients, from their terrestrial estimates. It was found that gravity anomalies could be recovered from strong signal without using any a-priori terrestrial information, i.e. considering their initial values as zero and also assigning them a zero weight matrix. While recovering them from weak signal, it was necessary to use the a-priori estimate of the standard deviation of the anomalies to form their a-priori diagonal weight matrix.

  20. Gravity anomalies, crustal structure and flexure of the lithosphere at the Baltimore Canyon Trough

    NASA Astrophysics Data System (ADS)

    Watts, A. B.

    1988-07-01

    Seismic and gravity anomaly data have been used to examine the long-term mechanical properties of the lithosphere beneath the Baltimore Canyon Trough, a 15 km deep sedimentary basin in the rifted U.S. Atlantic margin. Seismic data constrain the crustal structure at the time of rifting as well as the amount of sedimentation and erosion that has occurred. The gravity effect of the initial crustal structure, sedimentary loading and erosional unloading have been computed and compared to the observed free-air gravity anomaly. The best fitting model is one in which the elastic thickness of the lithosphere ( Te) changes at the East Coast magnetic anomaly. Landward of the anomaly, Te is significantly smaller than previously reported values for continental or oceanic lithosphere of the same thermal age. Seaward of the anomaly, however, Te follows the depth to the 450°C oceanic isotherm which also describes the response of oceanic lithosphere to seamount and oceanic island loads. These results are interpreted as indicating that the shelf part of the trough is underlain by continental lithosphere which, following rifting, did not acquire any significant long-term strength.

  1. Principal facts of gravity stations with gravity and magnetic profiles from the Southwest Nevada Test Site, Nye County, Nevada, as of January, 1982

    USGS Publications Warehouse

    Jansma, P.E.; Snyder, D.B.; Ponce, David A.

    1983-01-01

    Three gravity profiles and principal facts of 2,604 gravity stations in the southwest quadrant of the Nevada Test Site are documented in this data report. The residual gravity profiles show the gravity measurements and the smoothed curves derived from these points that were used in geophysical interpretations. The principal facts include station label, latitude, longitude, elevation, observed gravity value, and terrain correction for each station as well as the derived complete Bouguer and isostatic anomalies, reduced at 2.67 g/cm 3. Accuracy codes, where available, further document the data.

  2. Crustal Thickness and Oceanic Lithosphere Distribution in the Eastern Mediterranean from Satellite Gravity Anomaly Inversion

    NASA Astrophysics Data System (ADS)

    Cowie, L.; Kusznir, N. J.

    2010-12-01

    The distribution of oceanic and continental lithosphere in the eastern Mediterranean is not well understood. Gravity inversion, incorporating a lithosphere thermal gravity anomaly correction, has been used to map Moho depth, crustal thickness and continental lithosphere thinning factor for the eastern Mediterranean in order to determine the distribution of oceanic and continental lithosphere and the ocean-continent transition location. Data used in the gravity inversion are bathymetry, free-air gravity and sediment thickness data from Smith and Sandwell (1997), Sandwell and Smith (2009) and Laske and Masters (1997) respectively. Moho depths from the gravity inversion are dependent on the age of oceanic lithosphere and continental breakup because of the lithosphere thermal gravity correction; however, these ages are uncertain for the eastern Mediterranean. Gravity inversion sensitivities to break-up ages of 225Ma (late Triassic) and 100Ma (early Cretaceous) have been examined. Gravity inversion results show thin crust (5 - 10km thickness) for the Ionian Sea and the Herodotus Basin of the eastern Mediterranean consistent with these basins being underlain by oceanic or highly thinned continental crust. Predicted Moho depths from the gravity inversion are in agreement with published Ionian Sea ESP results (Voogd et al, 1992) and suggest a gravity inversion reference Moho depth increasing to the north, which we attribute to subduction dynamic subsidence. Calibration of gravity inversion Moho against ESP results show a trade-off between break-up age and reference Moho depth; a Cretaceous age ocean requires a larger Moho reference depth than a Triassic age ocean. Lithosphere thinning factor maps from gravity inversion for Africa do not show continuity between the Cretaceous African rift system (Benue Trough, Chad, CASZ and Sudan basins) and eastern Mediterranean basins. If the Ionian Sea is of Cretaceous age then it more probably links to Cretaceous rifting and sea

  3. 3D Inversion of Gravity Anomalies for the Interpretation of Sedimentary Basins using Variable Density Contrast

    NASA Astrophysics Data System (ADS)

    Ekinci, Yunus Levent; Ertekin, Can

    2015-04-01

    Concern about sedimentary basins is generally related to their genetic and economic significance. Analysis of sedimentary basins requires the acquisition of data through outcrop studies and subsurface investigations that encompass drilling and geophysics. These data are commonly analysed by computer-assisted techniques. One of these methods is based on analysing gravity anomalies to compute the depth of sedimentary basin-basement rock interface. Sedimentary basins produce negative gravity anomalies, because they have mostly lower densities than that of the surrounding basement rocks. Density variations in a sedimentary fill increase rapidly at shallower depths then gradually reach the density of surrounding basement rocks due to the geostatic pressure i.e. compaction. The decrease of the density contrast can be easily estimated by a quadratic function. Hence, if the densities are chosen properly and the regional background is removed correctly, the topographical relief of the sedimentary basin-basement rock interface might be estimated by the inversion of the gravity data using an exponential density-depth relation. Three dimensional forward modelling procedure can be carried out by introducing a Cartesian coordinate system, and placing vertical prisms just below observation points on the grid plane. Depth to the basement, namely depths to the bottom of the vertical prisms are adjusted in an iterative manner by minimizing the differences between measured and calculated residual gravity anomalies. In this study, we present a MATLAB-based inversion code for the interpretation of sedimentary basins by approximating the topographical relief of sedimentary basin-basement rock interfaces. For a given gridded residual gravity anomaly map, the procedure estimates the bottom depths of vertical prisms by considering some published formulas and assumptions. The utility of the developed inversion code was successfully tested on theoretically produced gridded gravity data set

  4. Covariant anomaly and Hawking radiation from the modified black hole in the rainbow gravity theory

    NASA Astrophysics Data System (ADS)

    Peng, Jun-Jin; Wu, Shuang-Qing

    2008-12-01

    Recently, Banerjee and Kulkarni (R. Banerjee, S. Kulkarni, arXiv: 0707. 2449 [hep-th]) suggested that it is conceptually clean and economical to use only the covariant anomaly to derive Hawking radiation from a black hole. Based upon this simplified formalism, we apply the covariant anomaly cancellation method to investigate Hawking radiation from a modified Schwarzschild black hole in the theory of rainbow gravity. Hawking temperature of the gravity’s rainbow black hole is derived from the energy-momentum flux by requiring it to cancel the covariant gravitational anomaly at the horizon. We stress that this temperature is exactly the same as that calculated by the method of cancelling the consistent anomaly.

  5. Deconstructing the shallow internal structure of the Moon using GRAIL gravity and LOLA topography

    NASA Astrophysics Data System (ADS)

    Zuber, M. T.

    2015-12-01

    Globally-distributed, high-resolution gravity and topography observations of the Moon from the Gravity Recovery and Interior Laboratory (GRAIL) mission and Lunar Orbiter Laser Altimeter (LOLA) instrument aboard the Lunar Reconnaissance Orbiter (LRO) spacecraft afford the unprecedented opportunity to explore the shallow internal structure of the Moon. Gravity and topography can be combined to produce Bouguer gravity that reveals the distribution of mass in the subsurface, with high degrees in the spherical harmonic expansion of the Bouguer anomalies sensitive to shallowest structure. For isolated regions of the lunar highlands and several basins we have deconstructed the gravity field and mapped the subsurface distribution of density anomalies. While specified spherical harmonic degree ranges can be used to estimate contributions at different depths, such analyses require considerable caution in interpretation. A comparison of filtered Bouguer gravity with forward models of disk masses with plausible densities illustrates the interdependencies of the gravitational power of density anomalies with depth and spatial scale. The results have implications regarding the limits of interpretation of lunar subsurface structure.

  6. Oceanwide gravity anomalies from Geos-3, Seasat and Geosat altimeter data

    NASA Technical Reports Server (NTRS)

    Rapp, Richard H.; Basic, Tomislav

    1992-01-01

    Three kinds of satellite altimeter data have been combined, along with 5 x 5 arcmin bathymetric data, to calculate a 0.125 deg ocean wide gridded set of 2.3 x 10 exp 6 free-air gravity anomalies. The procedure used was least squares collocation that yields the predicted anomaly and standard deviation. The value of including the bathymetric data was shown in a test around the Dowd Seamount where the root mean square (rms) difference between ship gravity measurements decreased from +/- 40 mgal to +/- 20 mgal when the bathymetry was included. Comparisons between the predicted anomalies and ship gravity data is described in three cases. In the Banda Sea the rms differences were +/- 20 mgal for two lines. In the South Atlantic rms differences over lines of 2000 km in length were +/- 7 mgal. For cruise data in the Antarctica region the discrepancies were +/- 12 mgal. Comparisons of anomalies derived from the Geosat geodetic mission data by Marks and McAdoo (1992) with ship dta gave differences of +/- 6 mgal showing the value of the much denser Geosat geodetic mission altimeter data.

  7. Negative gravity anomaly over spreading rift valleys: Mid-Atlantic Ridge at 26°N

    NASA Astrophysics Data System (ADS)

    Bowin, Carl; Milligan, Julie

    1985-03-01

    A pronounced negative free-air gravity anomaly commonly occurs over the median valley of slow spreading ocean ridges. Previous results, using Wiener filtering and cross-spectral analysis techniques for the Mid-Atlantic Ridge, obtained estimates of the elastic plate thickness in the range of 7-13 km and the existence of a residual negative gravity anomaly over the median rift valley, suggesting that the rift valley has a response function different than the remainder of the spreading ridge. In this paper we have improved the derivation of the topography-gravity admittance function for spreading ocean crust by carefully avoiding several sources of spectral splattering when processing the data: (1) selecting data from a cruise that followed a flowline of central North Atlantic relative plate motion and hence is least corrupted by fracture zones; and (2) accounting for the difference in distance between the gravity meter and the regional variation in elevation as the ridge crest is traversed. Improvements of lesser importance include the use of cubic splines to interpolate to equally spaced data rather than linear interpolation, and correction of the free-air anomaly values for long-wavelength variations of the indirect effect. Comparison of the resulting admittance function to elastic flexure response functions suggests an elastic plate thickness of about 8 km. The improved admittance function, when convolved with the ridge topography, provides a predicted gravity profile that accounts very well for the negative anomaly over the rift valley. Therefore, the isostatic response function for the rift valley is similar to that for the topography away from the rift valley.

  8. Lithospheric structure across the central Tien Shan constrained by gravity anomalies and joint inversions of receiver function and Rayleigh group velocity data

    NASA Astrophysics Data System (ADS)

    Li, Yonghua; Shi, Lei; Gao, Jiayi

    2016-04-01

    Shear wave velocity structure across the central Tien Shan orogeny was generated by jointly inverting Rayleigh wave phase and group velocity with teleseismic P-wave receiver functions at 40 broad band seismic stations of the MANAS project. The inferred seismic structure was validated by forward modeling of the complete Bouguer anomaly data. The joint inversion result reveals larger crust thicknesses beneath the Kokshaal (~68-72 km) and Kyrgyz ranges (~62-64 km), while other units have crustal thicknesses between 48 and 58 km. A fast velocity layer (Vs = 3.6-3.9 km/s) in the upper crust is found in some seismic stations within the Kazakh Shield. Our models show the presence of high velocity and density layers in the lowermost crust throughout the region, consistent with the presence of mafic/ultramafic lithologies. The large crustal thickness is associated with a thickened mafic layer in the lower crust, indicating that the thickened crust may be partly caused by magmatic underplating. The low velocity and density anomaly in the middle crust, and low upper mantle velocity observed in our model beneath the middle Tien Shan reflects the presence of partial melt in the crust due to the intrusion of hot mantle material. The lack of correlation between Moho depth and topography, together with the gravity results, suggests that the topographic compensation in the central Tien Shan is not confined to the crust. This requires significant support from the mantle to account for the relative high elevation of the middle Tien Shan.

  9. Application of Magsat lithospheric modeling in South America. Part 1: Processing and interpretation of magnetic and gravity anomaly data

    NASA Technical Reports Server (NTRS)

    Hinze, W. J.; Braile, L. W.; Vonfrese, R. R. B. (Principal Investigator); Keller, G. R.; Lidiak, E. G.

    1984-01-01

    Scalar magnetic anomaly data from MAGSAT, reduced to vertical polarization and long wavelength pass filtered free air gravity anomaly data of South America and the Caribbean are compared to major crustal features. The continental shields generally are more magnetic than adjacent basins, oceans and orogenic belts. In contrast, the major aulacogens are characterized by negative anomalies. Spherical earth magnetic modeling of the Amazon River and Takatu aulacogens in northeastern South America indicates a less magnetic crust associated with the aulacogens. Spherical earth modeling of both positive gravity and negative magnetic anomalies observed over the Mississippi Embayment indicate the presence of a nonmagnetic zone of high density material within the lower crust associated with the aulacogen. The MAGSAT scalar magnetic anomaly data and available free air gravity anomalies over Euro-Africa indicate several similar relationships.

  10. Preliminary Investigation of EarthScope EARS Derived MOHO Topography and Large Scale Faye Gravity Anomaly

    NASA Astrophysics Data System (ADS)

    Crain, K.; Holland, A. A.

    2013-12-01

    This is a preliminary investigation using the EarthScope EARS receiver functions in combination with the Faye gravity anomaly. This includes both qualitative and quantitative comparison of the large scale Faye anomaly with an expected 3D geology interpretation for the southern mid-continent U.S.A. The 3D geology interpretation consists of expected 3D topographies based on National Elevation Data, published formation elevations, measured and published basement topography with geology, and the expected MOHO topography calculated using the EARS estimated crustal thickness. The EARS automated receiver functions provides a large data set of automatically generated receiver functions and models of bulk crustal properties. These bulk crustal properties include crustal thickness, and Vp/Vs given an assumed Vp. The results from this automatic determination can be evaluated through the H-K stacking, and are often a good method to identify where there may be complex structure or poor quality data. Some a priori information is used to constrain the EARS crustal model. The observed Faye gravity anomaly is calculated using the observed gravity value at their observation location from the PACES gravity database and their extracted elevation from the national elevation data set. Then the expected Faye gravity is modeled using the expected 3D geology interpretation. The observed and modeled Faye gravity, along with the expected 3D geologic interpretation with its topographies and geology and their expected uncertainties are used in a simple 3D density inversion to evaluate the consistency of the estimated with the expected crust / MOHO interface. Areas with complex crustal geology and or inconsistent EARS data are identified as areas of higher uncertainty and require further study. Even areas with agreement between the expected MOHO topography and the Faye anomaly have interesting geology implications. For example: in central Oklahoma the 14 km deep Anadarko basin has a positive

  11. Preparation of Residual Gravity Maps for the Southern Cascade Mountains, Washington Using Fourier Analysis

    SciTech Connect

    Dishberger, Debra McLean

    1983-04-01

    This report represents a continuation of gravity work in the Cascade Mountains of Washington supported by the Division of Geology and Earth Resources since 1974. The purpose of this research has been collection of baseline gravity data for use in geothermal resource evaluation. Results of the Division's gravity studies to date are given in Danes and Phillips (1983a, 1983b). One of the problems encountered when analyzing gravity data is distinguishing between those parts of the data that represent geologic structures of interest, and those that do not. In many cases, the features of interest are relatively small, near-surface features, such as those sought in mineral, petroleum, or geothermal exploration. Gravity anomalies caused by such structures may be distorted or masked by anomalies caused by larger, deeper geologic structures. Gravity anomalies caused by relatively shallow, small geologic structures are termed residual anomalies. Those due to broad, deep-seated features can be described as regional anomalies. The purpose of this report is to describe a Fourier analysis method for separating residual and regional gravity anomalies from a complete Bouguer gravity anomaly field. The technique has been applied to gravity data from the Southern Cascade Mountains, Washington. Residual gravity anomaly maps at a scale of 1:250,000 are presented for various regional wavelength filters, and a power spectrum of the frequency components in the South Cascade gravity data is displayed. No attempt is made to interpret the results of this study in terms of geologic structures.

  12. Joint Inversion and Forward Modeling of Gravity and Magnetic Data in the Ismenius Region of Mars

    NASA Technical Reports Server (NTRS)

    Milbury, C. A.; Raymond, C. A.; Jewell, J. B.; Smrekar, S. E.; Schubert, G.

    2005-01-01

    The unexpected discovery of remanent crustal magnetism on Mars was one of the most intriguing results from the Mars Global Surveyor mission. The origin of the pattern of magnetization remains elusive. Correlations with gravity and geology have been examined to better understand the nature of the magnetic anomalies. In the area of the Martian dichotomy between 50 and 90 degrees E (here referred to as the Ismenius Area), we find that both the Bouguer and the isostatic gravity anomalies appear to correlate with the magnetic anomalies and a buried fault, and allow for a better constraint on the magnetized crust].

  13. Dynamic topography and gravity anomalies for fluid layers whose viscosity varies exponentially with depth

    NASA Technical Reports Server (NTRS)

    Revenaugh, Justin; Parsons, Barry

    1987-01-01

    Adopting the formalism of Parsons and Daly (1983), analytical integral equations (Green's function integrals) are derived which relate gravity anomalies and dynamic boundary topography with temperature as a function of wavenumber for a fluid layer whose viscosity varies exponentially with depth. In the earth, such a viscosity profile may be found in the asthenosphere, where the large thermal gradient leads to exponential decrease of viscosity with depth, the effects of a pressure increase being small in comparison. It is shown that, when viscosity varies rapidly, topography kernels for both the surface and bottom boundaries (and hence the gravity kernel) are strongly affected at all wavelengths.

  14. Gravity evidence for a shallow intrusion under Medicine Lake volcano, California.

    USGS Publications Warehouse

    Finn, C.; Williams, D.L.

    1982-01-01

    A positive gravity anomaly is associated with Medicine Lake volcano, California. Trials with different Bouguer reduction densities indicate that this positive anomaly cannot be explained by an inappropriate choice of Bouguer reduction density but must be caused by a subvolcanic body. After separating the Medicine Lake gravity high from the regional field, we were able to fit the 27mgal positive residual anomaly with a large, shallow body of high density contrast (+0.41g/cm3) and a thickness of 2.5km. We interpret this body to be an intrusion of dense material emplaced within the several-kilometres-thick older volcanic layer that probably underlies Medicine Lake volcano.-Authors

  15. Anomalies and Hawking fluxes from the black holes of topologically massive gravity

    NASA Astrophysics Data System (ADS)

    Porfyriadis, Achilleas P.

    2009-05-01

    The anomaly cancelation method proposed by Wilczek et al. is applied to the black holes of topologically massive gravity (TMG) and topologically massive gravito-electrodynamics (TMGE). Thus the Hawking temperature and fluxes of the ACL and ACGL black holes are found. The Hawking temperatures obtained agree with the surface gravity formula. Both black holes are rotating and this gives rise to appropriate terms in the effective U (1) gauge field of the reduced (1 + 1)-dimensional theory. It is found that the terms in this U (1) gauge field correspond exactly to the correct angular velocities on the horizon of both black holes as well as the correct electrostatic potential of the ACGL black hole. So the results for the Hawking fluxes derived here from the anomaly cancelation method, are in complete agreement with the ones obtained from integrating the Planck distribution.

  16. Improved gravity anomaly fields from retracked multimission satellite radar altimetry observations over the Persian Gulf and the Caspian Sea

    NASA Astrophysics Data System (ADS)

    Khaki, M.; Forootan, E.; Sharifi, M. A.; Awange, J.; Kuhn, M.

    2015-09-01

    Satellite radar altimetry observations are used to derive short wavelength gravity anomaly fields over the Persian Gulf and the Caspian Sea, where in situ and ship-borne gravity measurements have limited spatial coverage. In this study the retracking algorithm `Extrema Retracking' (ExtR) was employed to improve sea surface height (SSH) measurements that are highly biased in the study regions due to land contaminations in the footprints of the satellite altimetry observations. ExtR was applied to the waveforms sampled by the five satellite radar altimetry missions: TOPEX/POSEIDON, JASON-1, JASON-2, GFO and ERS-1. Along-track slopes have been estimated from the improved SSH measurements and used in an iterative process to estimate deflections of the vertical, and subsequently, the desired gravity anomalies. The main steps of the gravity anomaly computations involve estimating improved SSH using the ExtR technique, computing deflections of the vertical from interpolated SSHs on a regular grid using a biharmonic spline interpolation and finally estimating gridded gravity anomalies. A remove-compute-restore algorithm, based on the fast Fourier transform, has been applied to convert deflections of the vertical into gravity anomalies. Finally, spline interpolation has been used to estimate regular gravity anomaly grids over the two study regions. Results were evaluated by comparing the estimated altimetry-derived gravity anomalies (with and without implementing the ExtR algorithm) with ship-borne free air gravity anomaly observations, and free air gravity anomalies from the Earth Gravitational Model 2008 (EGM2008). The comparison indicates a range of 3-5 mGal in the residuals, which were computed by taking the differences between the retracked altimetry-derived gravity anomaly and the ship-borne data. The comparison of retracked data with ship-borne data indicates a range in the root-mean-square-error (RMSE) between approximately 1.8 and 4.4 mGal and a bias between 0

  17. Vertical and Horizontal Analysis of Crustal Structure of Southeastern Mediterranean and the Egyptian Coastal Zone, from Bouguer and Satellite Mission Data

    NASA Astrophysics Data System (ADS)

    Saleh, Salah

    2016-07-01

    The present Tectonic system of Southeastern Mediterranean is driven by the collision of the African and Eurasian plates, the Arabian Eurasian convergence and the displacement of the Anatolian Aegean microplate, which generally represents the characteristic of lithospheric structure of the region. In the scope of this study, Bouguer and the satellite gravity (satellite altimetry) anomalies of southeastern Mediterranean and North Eastern part of Egypt were used for investigating the lithospheric structures. Second order trend analyses were applied firstly to Bouguer and satellite altimetry data for examining the characteristic of the anomaly. Later, the vertical and horizontal derivatives applications were applied to the same data. Generally, the purpose of the applying derivative methods is determining the vertical and horizontal borders of the structure. According to the results of derivatives maps, the study area could mainly divided into important four tectonic subzones depending on basement and Moho depth maps. These subzones are distributed from south to the north as: Nile delta-northern Sinai zone, north Egyptian coastal zone, Levantine basin zone and northern thrusting (Cyprus and its surroundings) zone. These zones are separated from each other by horizontal tectonic boundaries and/or near-vertical faults that display the block-faulting tectonic style of this belt. Finally, the gravity studies were evaluated together with the seismic activity of the region. Consequently, the geodynamical structure of the region is examined with the previous studies done in the region. Thus, the current study indicates that satellite gravity mission data is a valuable source of data in understanding the tectonic boundary behavior of the studied region and that satellite gravity data is an important modern source of data in the geodynamical studies.

  18. Mean gravity anomalies and sea surface heights derived from GEOS-3 altimeter data

    NASA Technical Reports Server (NTRS)

    Rapp, R. H.

    1978-01-01

    Approximately 2000 GEOS-3 altimeter arcs were analyzed to improve knowledge of the geoid and gravity field. An adjustment procedure was used to fit the sea surface heights (geoid undulations) in an adjustment process that incorporated cross-over constraints. The error model used for the fit was a one or two parameter model which was designed to remove altimeter bias and orbit error. The undulations on the adjusted arcs were used to produce geoid maps in 20 regions. The adjusted data was used to derive 301 5 degree equal area anomalies and 9995 1 x 1 degree anomalies in areas where the altimeter data was most dense, using least squares collocation techniques. Also emphasized was the ability of the altimeter data to imply rapid anomaly changes of up to 240 mgals in adjacent 1 x 1 degree blocks.

  19. Gravity and magnetic anomaly modeling and correlation using the SPHERE program and Magsat data

    NASA Technical Reports Server (NTRS)

    Braile, L. W.; Hinze, W. J. (Principal Investigator); Vonfrese, R. R. B.

    1980-01-01

    The spherical Earth inversion, modeling, and contouring software were tested and modified for processing data in the Southern Hemisphere. Preliminary geologic/tectonic maps and selected cross sections for South and Central America and the Caribbean region are being compiled and as well as gravity and magnetic models for the major geological features of the area. A preliminary gravity model of the Andeas Beniff Zone was constructed so that the density columns east and west of the subducted plates are in approximate isostatic equilibrium. The magnetic anomaly for the corresponding magnetic model of the zone is being computed with the SPHERE program. A test tape containing global magnetic measurements was converted to a tape compatible with Purdue's CDC system. NOO data were screened for periods of high diurnal activity and reduced to anomaly form using the IGS-75 model. Magnetic intensity anomaly profiles were plotted on the conterminous U.S. map using the track lines as the anomaly base level. The transcontinental magnetic high seen in POGO and MAGSAT data is also represented in the NOO data.

  20. Spherical Earth analysis and modeling of lithospheric gravity and magnetic anomalies. Ph.D. Thesis - Purdue Univ.

    NASA Technical Reports Server (NTRS)

    Vonfrese, R. R. B.; Hinze, W. J.; Braile, L. W.

    1980-01-01

    A comprehensive approach to the lithospheric analysis of potential field anomalies in the spherical domain is provided. It has widespread application in the analysis and design of satellite gravity and magnetic surveys for geological investigation.

  1. Chapter 3: Circum-Arctic mapping project: New magnetic and gravity anomaly maps of the Arctic

    USGS Publications Warehouse

    Gaina, C.; Werner, S.C.; Saltus, R.; Maus, S.; Aaro, S.; Damaske, D.; Forsberg, R.; Glebovsky, V.; Johnson, K.; Jonberger, J.; Koren, T.; Korhonen, J.; Litvinova, T.; Oakey, G.; Olesen, O.; Petrov, O.; Pilkington, M.; Rasmussen, T.; Schreckenberger, B.; Smelror, M.

    2011-01-01

    New Circum-Arctic maps of magnetic and gravity anomalies have been produced by merging regional gridded data. Satellite magnetic and gravity data were used for quality control of the long wavelengths of the new compilations. The new Circum-Arctic digital compilations of magnetic, gravity and some of their derivatives have been analyzed together with other freely available regional and global data and models in order to provide a consistent view of the tectonically complex Arctic basins and surrounding continents. Sharp, linear contrasts between deeply buried basement blocks with different magnetic properties and densities that can be identified on these maps can be used, together with other geological and geophysical information, to refine the tectonic boundaries of the Arctic domain. ?? 2011 The Geological Society of London.

  2. Principal Facts for Gravity Data Collected in Wisconsin: A Web Site and CD-ROM for Distribution of Data

    USGS Publications Warehouse

    Snyder, Stephen L.; Geister, Daniel W.; Daniels, David L.; Ervin, C. Patrick

    2004-01-01

    Principal facts for 40,488 gravity stations covering the entire state of Wisconsin are presented here in digital form. This is a compilation of previously published data collected between 1948 and 1992 from numerous sources, along with over 10,000 new gravity stations collected by the USGS since 1999. Also included are 550 gravity stations from previously unpublished sources. Observed gravity and complete-Bouguer gravity anomaly data for this statewide compilation are included here. Altogether, 14 individual surveys are presented here.

  3. Probing the Lunar Polar Crust with GRAIL Gravity

    NASA Astrophysics Data System (ADS)

    Smith, D. E.; Zuber, M. T.; Goossens, S. J.; Rowlands, D. D.; Neumann, G. A.; Mazarico, E.; Genova, A.; Lemoine, F. G.

    2015-12-01

    The lunar polar crust, from latitude ±80° to the pole, exhibits Bouguer gravity anomalies that result from crustal density variations of order ±45 mGal in the south and ±25 mGal in the north, bandpass filtered to wavelengths representing the top 50 km. Evident in the Bouguer gravity at both poles are the signatures of a few large craters and basins. But at both poles, the Bouguer map also displays a large number of small, rather sinuous features, some outlining crater rims and some structures on crater floors, that are distributed more or less uniformly across the region. The root mean square (rms) variation over the 10° radius cap is less than 11 mGals at the south pole and less than 7 mGals in the north. This difference reflects the greater crustal complexity in the south compared to the north, but these magnitudes are approximately 10% of the total field in the polar regions, indicating that substantial density anomalies exist below 50 km depth. Modeling the crustal anomalies in the top 50 km by density contrasts at various depths suggest the rms magnitudes can be explained by small local variations in porosity, or possibly the presence of H2O at concentrations of a few percent. The required concentration increases with depth for a given volume but the possibility that the source of the polar anomalies includes small concentrations of H2O in the crust, however, cannot be ruled out.

  4. Joint Interpretation of Bathymetric and Gravity Anomaly Maps Using Cross and Dot-Products.

    NASA Astrophysics Data System (ADS)

    Jilinski, Pavel; Fontes, Sergio Luiz

    2010-05-01

    0.1 Summary We present the results of joint map interpretation technique based on cross and dot-products applied to bathymetric and gravity anomaly gradients maps. According to the theory (Gallardo, Meju, 2004) joint interpretation of different gradient characteristics help to localize and empathize patterns unseen on one image interpretation and gives information about the correlation of different spatial data. Values of angles between gradients and their cross and dot-product were used. This technique helps to map unseen relations between bathymetric and gravity anomaly maps if they are analyzed separately. According to the method applied for the southern segment of Eastern-Brazilian coast bathymetrical and gravity anomaly gradients indicates a strong source-effect relation between them. The details of the method and the obtained results are discussed. 0.2 Introduction We applied this method to investigate the correlation between bathymetric and gravity anomalies at the southern segment of the Eastern-Brazilian coast. Gridded satellite global marine gravity data and bathymetrical data were used. The studied area is located at the Eastern- Brazilian coast between the 20° W and 30° W meridians and 15° S and 25° S parallels. The volcanic events responsible for the uncommon width of the continental shelf at the Abrolhos bank also were responsible for the formation of the Abrolhos islands and seamounts including the major Vitoria-Trindade chain. According to the literature this volcanic structures are expected to have a corresponding gravity anomaly (McKenzie, 1976, Zembruscki, S.G. 1979). The main objective of this study is to develop and test joint image interpretation method to compare spatial data and analyze its relations. 0.3 Theory and Method 0.3.1 Data sources The bathymetrical satellite data were derived bathymetry 2-minute grid of the ETOPO2v2 obtained from NOAA's National Geophysical Data Center (http://www.ngdc.noaa.gov). The satellite marine gravity 1

  5. Calculation of gravity and magnetic anomalies along profiles with end corrections and inverse solutions for density and magnetization

    USGS Publications Warehouse

    Cady, John W.

    1977-01-01

    A computer program is presented which performs, for one or more bodies, along a profile perpendicular to strike, both forward calculations for the magnetic and gravity anomaly fields and independent gravity and magnetic inverse calculations for density and susceptibility or remanent magnetization.

  6. Lunar floor-fractured craters as magmatic intrusions: Geometry, modes of emplacement, associated tectonic and volcanic features, and implications for gravity anomalies

    NASA Astrophysics Data System (ADS)

    Jozwiak, Lauren M.; Head, James W.; Wilson, Lionel

    2015-03-01

    , the intrusion concentrates bending primarily at the periphery, resulting in a flat, tabular intrusion. We predict that this process will result in concentric fractures over the region of greatest bending. This location is close to the crater wall in large, flat-floored craters, as observed in the crater Humboldt, and interior to the crater over the domed floor in smaller craters, as observed in the crater Vitello. A variety of volcanic features are predicted to be associated with the solidification and degassing of the intrusion; these include: (1) surface lava flows associated with concentric fractures (e.g., in the crater Humboldt); (2) vents with no associated pyroclastic material, from the deflation of under-pressurized magmatic foam (e.g., the crater Damoiseau); and (3) vents with associated pyroclastic deposits from vulcanian eruptions of highly pressurized magmatic foam (e.g., the crater Alphonsus). The intrusion of basaltic magma beneath the crater is predicted to contribute a positive component to the Bouguer gravity anomaly; we assess the predicted Bouguer anomalies associated with FFCs and outline a process for their future interpretation. We conclude that our proposed mechanism serves as a viable formation process for FFCs and accurately predicts numerous morphologic, morphometric, and geophysical features associated with FFCs. These predictions can be further tested using GRAIL (Gravity Recovery and Interior Laboratory) data.

  7. The gravity signature of mantle uplift from impact modeling craters on the Moon

    NASA Astrophysics Data System (ADS)

    Milbury, Colleen; Johnson, Brandon C.; Melosh, H. Jay; Collins, Gareth S.; Blair, David M.; Soderblom, Jason M.; Zuber, Maria T.

    2014-11-01

    NASA’s dual Gravity Recovery and Interior Laboratory (GRAIL) spacecraft have globally mapped the lunar gravity field at unprecedented resolution; this has enabled the study of lunar impact craters of all sizes and ages. Soderblom et al. [2014, LPSC abstract #1777] calculated the residual Bouguer anomalies for ~2700 craters 27-184 km in diameter (D). They found that the residual central Bouguer anomaly of craters smaller than 100 km is essentially zero, that there is a transition for 100-150 km, and that craters larger than 184 km have a positive residual Bouguer anomaly that increases with increasing crater size. We use the iSALE shock physics hydrocode to model crater formation, including the effects of porosity and dilatancy (shear bulking). We use strength parameters of gabbroic anorthosite for a 35-km-thick crust, and dunite for the mantle. Our dunite impactors range in size from 6-30 km, which produce craters 86-450 km in diameter. We calculate the Bouguer gravity anomaly due solely to mantle uplift. We eliminate the effects of pressure and temperature on density by setting the output densities from the simulations to 2550 kg/m^3 if they are below the cutoff value of 3000 kg/m^3, and 3220 kg/m^3 if they are above. We compare our modeling results to gravity data from GRAIL. We find that the crater size at which mantle uplift dominates the crater gravity occurs at a crater diameter that is close to the complex crater to peak-ring basin transition. This is in agreement with the observed trend reported by Soderblom et al. [2014, LPSC abstract #1777].

  8. Gravity Survey of the Carson Sink - Data and Maps

    DOE Data Explorer

    Faulds, James E.

    2013-12-31

    A detailed gravity survey was carried out for the entire Carson Sink in western Nevada (Figure 1) through a subcontract to Zonge Engineering, Inc. The Carson Sink is a large composite basin containing three known, blind high‐temperature geothermal systems (Fallon Airbase, Stillwater, and Soda Lake). This area was chosen for a detailed gravity survey in order to characterize the gravity signature of the known geothermal systems and to identify other potential blind systems based on the structural setting indicated by the gravity data. Data: Data were acquired at approximately 400, 800, and 1600 meter intervals for a total of 1,243 stations. The project location and station location points are presented in Figure 14. The station distribution for this survey was designed to complete regional gravity coverage in the Carson Sink area without duplication of available public and private gravity coverage. Gravity data were acquired using a Scintrex CG‐5 gravimeter and a LaCoste and Romberg (L&R) Model‐G gravimeter. The CG‐5 gravity meter has a reading resolution of 0.001 milligals and a typical repeatability of less than 0.005 milligals. The L&R gravity meter has a reading resolution of 0.01 milligals and a typical repeatability of 0.02 milligals. The basic processing of gravimeter readings to calculate through to the Complete Bouguer Anomaly was made using the Gravity and Terrain Correction software version 7.1 for Oasis Montaj by Geosoft LTD. Results: The gravity survey of the Carson Sink yielded the following products. Project location and station location map (Figure 14). Complete Bouguer Anomaly @ 2.67 gm/cc reduction density. Gravity Complete Bouguer Anomaly at 2.50 g/cc Contour Map (Figure 15). Gravity Horizontal Gradient Magnitude Shaded Color Contour Map. Gravity 1st Vertical Derivative Color Contour Map. Interpreted Depth to Mesozoic Basement (Figure 16), incorporating drill‐hole intercept values. Preliminary Interpretation of Results: The Carson Sink

  9. Subsurface structure of Teboursouk and El Krib plains (dome zone, northern Tunisia) by gravity analysis

    NASA Astrophysics Data System (ADS)

    Hadhemi, Balti; Fatma, Hachani; Ali, Kadri; Mohamed, Gasmi

    2016-07-01

    Gravity data was used to investigate sub-surface structure of the Teboursouk and El Krib plains belonging to the dome zone in the Northwest of Tunisia. Analysis of the gravity data included the computation of the Bouguer anomaly, the horizontal and vertical gravity gradients, the upward continuations, Euler deconvolution and analytic signal of high-resolution. The Bouguer anomaly map (d = 2.4 g cm-3) has provided information on the variation of the underground density and shown contrasting anomalous zones. The treatments applied to the Bouguer anomaly map have detected new deep faults and provided details on their dips and depths (exceeding 1500 m per places). Statistical analysis of the gravity data filtering shows that the study area is divided by four major faults with NW-SE, NE-SW, E-W and N-S trends. These faults have contributed to the structuring of the area. The results provide confirmation of some faults already recognized or inferred from the previous structural studies, and specify their depths and dips. While large number of new faults that remained undetected until now, have been highlighted.

  10. Crustal structure beneath the southern Appalachians: nonuniqueness of gravity modeling

    USGS Publications Warehouse

    Hutchinson, Deborah R.; Grow, John A.; Klitgord, Kim D.

    1983-01-01

    Gravity models computed for a profile across the long-wavelength paired negative-positive Bouguer anomalies of the southern Appalachian Mountains show that the large negative anomaly can be explained by a crustal root zone, whereas the steep gradient and positive anomaly east of the root may be explained equally well by three different geometries: a suture zone, a mantle upwarp, or a shallow body. Seismic data support the existence of a mountain root but are inadequate to resolve differences among the three possible geometries for the positive anomaly. The presence of outcropping mafic and ultramafic rocks in the southern Appalachians and the inferred tectonic history of the Appalachian orogen are most consistent with the suture-zone model. Crust similar to continental crust probably exists beneath the Coastal Plain and inner continental shelf where the gravity anomalies return to near-zero values.

  11. A harmonic analysis of lunar gravity

    NASA Technical Reports Server (NTRS)

    Bills, B. G.; Ferrari, A. J.

    1980-01-01

    An improved model of lunar global gravity has been obtained by fitting a sixteenth-degree harmonic series to a combination of Doppler tracking data from Apollo missions 8, 12, 15, and 16, and Lunar Orbiters 1, 2, 3, 4, and 5, and laser ranging data to the lunar surface. To compensate for the irregular selenographic distribution of these data, the solution algorithm has also incorporated a semi-empirical a priori covariance function. Maps of the free-air gravity disturbance and its formal error are presented, as are free-air anomaly and Bouguer anomaly maps. The lunar gravitational variance spectrum has the form V(G; n) = O(n to the -4th power), as do the corresponding terrestrial and martian spectra. The variance spectra of the Bouguer corrections (topography converted to equivalent gravity) for these bodies have the same basic form as the observed gravity; and, in fact, the spectral ratios are nearly constant throughout the observed spectral range for each body. Despite this spectral compatibility, the correlation between gravity and topography is generally quite poor on a global scale.

  12. Sedimentary basin analysis using airborne gravity data: a case study from the Bohai Bay Basin, China

    NASA Astrophysics Data System (ADS)

    Li, Wenyong; Liu, Yanxu; Zhou, Jianxin; Zhou, Xihua; Li, Bing

    2015-12-01

    In this paper, we discuss the application of an airborne gravity survey to sedimentary basin analysis. Using high-precision airborne gravity data constrained by drilling and seismic data from the Bohai Bay Basin in eastern China, we interpreted faults, structural elements, sedimentary thickness, structural styles and local structures (belts) in the central area of the Basin by the wavelet transform method. Subsequently, these data were subtracted from the Bouguer gravity to calculate the residual gravity anomalies. On this basis, the faults were interpreted mainly by linear zones of high gravity gradients and contour distortion, while the sedimentary thicknesses were computed by the Euler deconvolution. The structural styles were identified by the combination of gravity anomalies and the local structures interpreted by the first vertical derivative of the residual gravity. The results showed evidence for seven faults, one sag and ten new local structure belts.

  13. Pre-impact crustal porosity and its effect on the gravity signature of lunar craters

    NASA Astrophysics Data System (ADS)

    Milbury, Colleen; Johnson, Brandon C.; Melosh, H. Jay; Collins, Gareth C.; Blair, David M.; Soderblom, Jason M.; Zuber, Maria T.

    2015-04-01

    NASA's dual Gravity Recovery and Interior Laboratory (GRAIL) spacecraft have globally mapped the lunar gravity field at unprecedented resolution. Soderblom et al. [2015] made a comprehensive analysis of the residual and central uplift Bouguer gravity anomalies associated with more than 5200 lunar craters. There were two main observations that are related to the work presented here: 1) craters less than ~150 km in diameter (D) have a residual Bouguer anomaly (BA) that is near zero on average (although a negative trend is observed), but have both positive and negative anomalies that vary by approximately ±25 mGal about the mean, and, 2) there is a transition at which the central uplift BA becomes positive and increases with D. Craters that are located in the maria and South Pole-Aitken (SPA) basin were excluded from the analysis because they tend to have more negative signatures than highlands craters. These gravitational signatures contrast with the invariably negative gravity anomalies associated with terrestrial craters. In this study, we investigate pre-impact porosity by modeling crater formation using the iSALE hydrocode, including a new approach to include dilatancy, to determine their effects on the gravity signature of craters. We calculated the BA for the simulations, but due to mantle uplift alone. We find that the magnitude of the BA increases with increasing porosity, and that variable initial porosity of the lunar crust can explain why craters on the Moon exhibit both positive and negative Bouguer anomalies. This can also explain the observed negative residual BA associated with craters formed in the lunar maria and SPA (and associated melt sheet) because they are typically less porous than the highlands crust. Gravity anomalies due to mantle uplift reproduce the observed transition from zero to a positive central uplift BA, which coincides with the morphological transition from complex craters to peak-ring basins.

  14. Gravity anomalies and the structure of western Tibet and the southern Tarim Basin

    NASA Technical Reports Server (NTRS)

    Lyon-Caen, H.; Molnar, P.

    1984-01-01

    Gravity anomalies across the western part of the Tarim Basin and the Kunlun mountain belt show that this area is not in local isostatic equilibrium. These data can be explained if a strong plate underlying the Tarim Basin extends southwestward beneath the belt at least 80 km and supports part of the topography of northwest Tibet. This corroborates Norin's inference that late Tertiary crustal shortening has occurred in this area by southward underthrusting of the Tarim Basin beneath the Kunlun. This study places a lower bound on the amount of underthrusting.

  15. Interpretation of Gravity Anomalies with the Normalized Full Gradient (NFG) Method and an Example

    NASA Astrophysics Data System (ADS)

    Aydin, Ali

    2007-12-01

    The Normalized Full Gradient (NFG) method which was put forward about 50 years ago has been used for downward continuation of gravity potential data, especially in the former Union of Soviet Socialist Republics. This method nullifies perturbations due to the passage of mass depth during downward continuation. The method depends on the downwards analytical continuation of normalized full gradient values of gravity data. Analytical continuation discriminates certain structural anomalies which cannot be distinguished in the observed gravity field. This method has been used in various petroleum and tectonic studies. The Trapeze method was used for the determination of Fourier coefficients during the application of this method. No other techniques for calculating these coefficients have been used. However, the Filon method was used for the determination of Fourier coefficients during the application of the NFG method in this work. This method, rather than the Trapeze method, should be preferred for indicating abnormal mass resources at the lower harmonics. In this study, the NFG method using the Filon method has been applied the first time to theoretical models of gravity profiles as example field at the Hasankale-Horasan petroleum exploration province where successful results were achieved. Hydrocarbon presence was shown on the NFG sections by the application of NFG downward continuation operations on theoretical models. Important signs of hydrocarbon structure on the NFG section for field and model data at low harmonics are obtained more effectively using this method.

  16. Modeling of shallow structures in the Cappadocia region using gravity and aeromagnetic anomalies

    NASA Astrophysics Data System (ADS)

    Kosaroglu, Sinan; Buyuksarac, Aydin; Aydemir, Attila

    2016-07-01

    In this study, shallow structures and bodies creating gravity and magnetic anomalies in the Cappadocia Volcanic Complex region in central Anatolia were investigated in order to determine the tectonic origin and structural setting of young volcanic units. The shallow geological structures in the region are depressions filled with mainly low-density, loose volcano-clastics and ignimbrite sheets associated with the continental Neogene deposits. These units together with other volcanic products are originated from the large Neogene and Quaternary volcanoes of the central Anatolia, particularly in the Cappadocia region. At first, spectral analysis to obtain the cut-off frequencies for the high-pass filter was performed in this investigation. Then, gravity and magnetic data were high-pass filtered to remove the deep and regional effects on anomalies and to unveil only shallow structures' effects. Subsequently, upward and downward continuations were carried out to determine how these shallow structures influence the total anomalies and their contribution in the confining total potential field. In addition, three and two dimensional gravity models (3D and 2D) of the study area were also constructed to obtain the bottom depth of shallow bodies. According to spectral analysis results, shallow structures could be separated into two groups from the power spectrums and bottom depth of deeper structure was commonly determined about 2 km in gravity and magnetic spectrum, both. More shallow structure is at the depth around 0.317 km according to the gravity power spectrum. Obviously, 3D and 2D models are consistent with the spectral analysis results for the deeper unit depth. A circular, large depression (70 × 50 km2) surrounds Mount Melendiz with a 1-2.7 km depth range (2 km in average). Because the depressions around the central volcanoes of Mount Melendiz and Mount Hasan cover very large areas in the basin scale, the shallow and low-density volcanic units can hardly be claimed

  17. Genesis of the largest Amazonian wetland in northern Brazil inferred by morphology and gravity anomalies

    NASA Astrophysics Data System (ADS)

    Rossetti, Dilce de Fátima; Cassola Molina, Eder; Cremon, Édipo Henrique

    2016-08-01

    The Pantanal Setentrional (PS) is the second largest wetland in Brazil, occurring in a region of northern Amazonia previously regarded as part of the intracratonic Solimões Basin. However, while Paleozoic to Neogene strata are recorded in this basin, the PS constitutes a broad region with an expressive record of only Late Pleistocene and Holocene deposits. The hypothesis investigated in the present work is if these younger deposits were formed within a sedimentary basin having a geological history separated from the Solimões Basin. Due to the location in a remote region of low accessibility, the sedimentary fill of the PS wetland remains largely unknown in subsurface. In the present work, we combine geomorphological and gravity data acquired on a global basis by several satellite gravity missions to approach the geological context of this region. The results revealed a wetland characterized in surface by a low-lying terrain with wedge shape and concave-up geometry that is in sharp contact with highland areas of Precambrian rocks of the Guiana Shield. Such contact is defined by a series of mainly NE- or NW-trending straight lineaments that eventually extend into both the Guiana Shield and the PS wetland. Also of relevance is that a great part of the PS wetland sedimentary cover consists of dominantly sandy deposits preserved as residual paleo-landforms with triangular shapes previously related to megafan depositional systems. These are distributed radially at the northern margin of the PS, with axis toward basement rocks and fringes toward the wetland's center, the latter containing the largest megafan landform. The analysis of gravity anomaly data revealed a main NNE-trending chain ∼500 km in length defined by high gravity values (i.e., up to 60 mGal); these are bounded by negative anomalies as low as -90 mGal. The chain with positive gravity anomaly marks the center of a subsiding area having a geological evolution that differs from the adjacent intracratonic

  18. Anomalies.

    ERIC Educational Resources Information Center

    Online-Offline, 1999

    1999-01-01

    This theme issue on anomalies includes Web sites, CD-ROMs and software, videos, books, and additional resources for elementary and junior high school students. Pertinent activities are suggested, and sidebars discuss UFOs, animal anomalies, and anomalies from nature; and resources covering unexplained phenonmenas like crop circles, Easter Island,…

  19. Principal facts for gravity stations in the Elko, Steptoe Valley, Coyote Spring Valley, and Sheep Range areas, eastern and southern Nevada

    USGS Publications Warehouse

    Berger, D.L.; Schaefer, D.H.; Frick, E.A.

    1990-01-01

    Principal facts for 537 gravity stations in the carbonate-rock province of eastern and southern Nevada are tabulated and presented. The gravity data were collected in support of groundwater studies in several valleys. The study areas include the Elko area, northern Steptoe Valley, Coyote Spring Valley, and the western Sheep Range area. The data for each site include values for latitude, longitude, altitude, observed gravity, free- air anomaly, terrain correction, and Bouguer anomaly (calculated at a bedrock density of 2.67 g/cu cm. (USGS)

  20. Gravity Anomaly Between Immature And Mature Subduction Zones In The Western Pacific And Its Implications For Subduction Evolution

    NASA Astrophysics Data System (ADS)

    Kim, Y.; Lee, S.

    2008-12-01

    From immature to mature subduction zones, the western Pacific is a key area to investigate subduction evolution. Among them, the Yap and Mussau trenches located in the boundary of Caroline plate and the Hjort trench to the south of New Zealand are considered as immature subduction zones. The common geological features of immature subduction zones include: (1) a short trench-arc distance, (2) the lack of Wadati-Benioff zone, and (3) the absence of arc volcanism triggered by subducting slab. On the other hand, the Izu-Bonin- Mariana and Tonga-Kermadec trenches are well-developed or mature subduction zones characterized by active arc volcanism and deep earthquakes. We compare two end-members, immature and mature subduction zones, with gravity anomaly derived from satellite altimetry which has sufficient accuracy for this kind of regional study. The isostatic residual gravity anomalies show that the width of non-isostatically- compensated region of the mature subduction zone is substantially wider than that of immature ones. Moreover, when we removed the gravitational effects due to the seafloor from the free-air gravity anomaly, a large difference was found between the immature and mature subduction zones in the overriding plate side. In the mature subduction zones, a low gravity anomaly of ~200-250 mGals can be found in the overriding plate which differs from the immature subduction zones. We discuss the possible causes of the low gravity anomaly including: (1) serpentinization in the upper mantle; (2) presence of partial melt in the mantle wedge; (3) difference in the density structure between the overriding and subducting plates in terms of slab age and cooling history; and (4) thickened crust or anomalous crustal structure beneath the arc. Serpentinization cannot explain the low gravity anomaly at ~150-200 km from the trench. Also, the difference of gravity anomaly due to the difference of the slab age is insufficient to account for the total anomaly. In this

  1. Interpretation of gravity and magnetic anomalies at Lake Rotomahana: Geological and hydrothermal implications

    NASA Astrophysics Data System (ADS)

    Caratori Tontini, F.; de Ronde, C. E. J.; Scott, B. J.; Soengkono, S.; Stagpoole, V.; Timm, C.; Tivey, M.

    2016-03-01

    We investigate the geological and hydrothermal setting at Lake Rotomahana, using recently collected potential-field data, integrated with pre-existing regional gravity and aeromagnetic compilations. The lake is located on the southwest margin of the Okataina Volcanic Center (Haroharo caldera) and had well-known, pre-1886 Tarawera eruption hydrothermal manifestations (the famous Pink and White Terraces). Its present physiography was set by the caldera collapse during the 1886 eruption, together with the appearance of surface activities at the Waimangu Valley. Gravity models suggest that subsidence associated with the Haroharo caldera is wider than the previously mapped extent of the caldera margins. Magnetic anomalies closely correlate with heat-flux data and surface hydrothermal manifestations and indicate that the west and northwestern shore of Lake Rotomahana are characterized by a large, well-developed hydrothermal field. The field extends beyond the lake area with deep connections to the Waimangu area to the south. On the south, the contact between hydrothermally demagnetized and magnetized rocks strikes along a structural lineament with high heat-flux and bubble plumes which suggest hydrothermal activity occurring west of Patiti Island. The absence of a well-defined demagnetization anomaly at this location suggests a very young age for the underlying geothermal system which was likely generated by the 1886 Tarawera eruption. Locally confined intense magnetic anomalies on the north shore of Lake Rotomahana are interpreted as basalt dikes with high magnetization. Some appear to have been emplaced before the 1886 Tarawera eruption. A dike located in proximity of the southwest lake shore may be related to the structural lineament controlling the development of the Patiti geothermal system, and could have been originated from the 1886 Tarawera eruption.

  2. 3D free-air gravity anomaly modeling for the Southeast Indian Ridge

    NASA Astrophysics Data System (ADS)

    Girolami, Chiara; Heyde, Ingo; Rinaldo Barchi, Massimiliano; Pauselli, Cristina

    2016-04-01

    In this study we analyzed the free-air gravity anomalies measured on the northwestern part of the Southeast Indian Ridge (hereafter SEIR) during the BGR cruise INDEX2012 with RV FUGRO GAUSS. The survey area covered the ridge from the Rodriguez Triple Junction along about 500 km towards the SSE direction. Gravity and magnetic data were measured along 65 profiles with a mean length of 60 km running approximately perpendicular to the ridge axis. The final gravity data were evaluated every 20 seconds along each profile. This results in a sampling interval of about 100 m. The mean spacing of the profiles is about 7 km. Together with the geophysical data also the bathymetry was measured along all profiles with a Kongsberg Simrad EM122 multibeam echosounder system. Previous studies reveal that the part of the ridge covered by the high resolution profiles is characterized by young geologic events (the oldest one dates back to 1 Ma) and that the SEIR is an intermediate spreading ridge. We extended the length of each profile to the area outside the ridge, integrating INDEX2012 high resolution gravity and bathymetric data with low resolution data derived from satellite radar altimeter measurements. The 3D forward gravity modeling made it possible to reconstruct a rough crustal density model for an extended area (about 250000 km2) of the SEIR. We analyzed the gravity signal along those 2D sections which cross particular geological features (uplifted areas, accommodation zones, hydrothermal fields and areas with hints for extensional processes e.g. OCCs) in order to establish a correlation between the gravity anomaly signal and the surface geology. We started with a simple "layer-cake" geologic model consisting of four density bodies which represent the sea, upper oceanic crust, lower oceanic crust and the upper mantle. Considering that in the study area the oceanic crust is young, we did not include the sediment layer. We assumed the density values of these bodies considering

  3. Interpretation of subsurface structure using gravity data from region of Appalachian ultradeep hole

    SciTech Connect

    Williams, R.T.; Favret, P.; Fabbri, L.; Chavez-Perez, S.

    1986-05-01

    More than 5000 new gravity measurements have been made over an area of 7500 km/sup 2/ in the region of the proposed ultradeep core hole in the southern Appalachians (ADCOH). Data were obtained mostly at surveyed elevations at approximately 0.5-km intervals along highways, and county and US Forest Service roads in the study area. The data have been reduced to simple Bouguer anomaly values using a standard crustal density of 2.67 g/cc and the International Gravity Formula of 1967. Simple Bouguer anomaly values range from about -10 to -80 mgal within the study area. Profiles crossing the outcrop of the Brevard fault zone (BFZ) at different locations reveal a characteristic gravity signature, with a decrease in gravity of more than 1.5 mgal. A profile along the route of ADCOH seismic line 3, located along US Highway 64 west of Hayesville, North Carolina, crosses a gravity high with an amplitude of more than 50 mgal. A contour map of simple Bouguer anomaly values reveals a linear gravity high of about 4 mgal, trending about N10/sup 0/E, that crosses ADCOH seismic line 1 northwest of Westminster, South Carolina, and seismic line 3 at its intersection with the BFZ. This anomaly correlates with a family of basement faults having more than 0.5 km of throw, seen on both seismic lines 1 and 3, and is evidence that these faults are oblique to both the trend of surface structure and the direction of the seismic profiles. Low gravity values are observed near the Shooting Creek window and Tallulah Falls dome, indicating that these structures may be cored by low-density, possibly sedimentary rocks.

  4. Relation of MAGSAT and Gravity Anomalies to the Main Tectonic Provinces of South America. M.S. Thesis

    NASA Technical Reports Server (NTRS)

    Yuan, D. W.

    1984-01-01

    Magnetic anomalies of the South American continent are generally more positive and variable than the oceanic anomalies. There is better correlation between the magnetic anomalies and the major tectonic elements of the continents than between the anomalies and the main tectonic elements of the adjacent oceanic areas. Oceanic areas generally show no direct correlation to the magnetic anomalies. Precambrian continental shields are mainly more magnetic than continental basins and orogenic belts. Shields differ markedly from major aulacogens which are generally characterized by negative magnetic anomalies and positive gravity anomalies. The Andean orogenic belt shows rather poor correlation with the magnetic anomalies. The magnetic data exhibit instead prominent east-west trends, which although consistent with some tectonic features, may be related to processing noise derived from data reduction procedures to correct for external magnetic field effects. The pattern over the Andes is sufficiently distinct from the generally north trending magnetic anomalies occurring in the adjacent Pacific Ocean to separate effectively the leading edge of the South American Plate from the Nazea Plate. Eastern South America is characterized by magnetic anomalies which commonly extend across the continental margin into the Atlantic Ocean.

  5. Preimpact porosity controls the gravity signature of lunar craters

    NASA Astrophysics Data System (ADS)

    Milbury, C.; Johnson, B. C.; Melosh, H. J.; Collins, G. S.; Blair, D. M.; Soderblom, J. M.; Nimmo, F.; Bierson, C. J.; Phillips, R. J.; Zuber, M. T.

    2015-11-01

    We model the formation of lunar complex craters and investigate the effect of preimpact porosity on their gravity signatures. We find that while preimpact target porosities less than ~7% produce negative residual Bouguer anomalies (BAs), porosities greater than ~7% produce positive anomalies whose magnitude is greater for impacted surfaces with higher initial porosity. Negative anomalies result from pore space creation due to fracturing and dilatant bulking, and positive anomalies result from destruction of pore space due to shock wave compression. The central BA of craters larger than ~215 km in diameter, however, are invariably positive because of an underlying central mantle uplift. We conclude that the striking differences between the gravity signatures of craters on the Earth and Moon are the result of the higher average porosity and variable porosity of the lunar crust.

  6. Gravity anomalies, flexure and mantle rheology seaward of Circum-Pacific trenches

    NASA Astrophysics Data System (ADS)

    Hunter, J.; Watts, A. B.

    2016-07-01

    We have used ensemble averages of satellite-derived free-air gravity anomaly data, together with inverse modelling techniques, to determine the effective elastic thickness, Te, of circum-Pacific subducting oceanic lithosphere and its relationship to plate age. Synthetic modelling tests show that Te can be recovered best using gravity anomaly, rather than bathymetry, data and profiles that are at least 750 km long. Inverse modeling based on a uniform Te elastic plate suggests that Te increases with age of the subducting oceanic lithosphere and is given approximately by the depth to the 390 ± 10°C oceanic isotherm based on a cooling plate model. Misfits between the observed and calculated gravity anomalies are significantly improved if a mechanically weak zone is included between the trench axis and the outer rise. This weak zone is coincident with observations of bend-faulting and seismicity. Inverse modelling shows that Te landward of the outer rise is generally 40-65% less than the Te seaward of the outer rise. Both landward and seaward Te increases with age of the lithosphere and are given by the depth to the 342-349°C and 671-714°C oceanic isotherm respectively. A dependence of Te on age is consistent with models for the cooling of oceanic lithosphere as it moves away from a mid-ocean ridge and the temperature-dependent ductile creep of oceanic lithospheric minerals such as olivine. By comparing the observed Te to the predicted Te based on laboratory-derived yield strength envelopes and an assumption of elastic-perfectly plastic deformation, we have attempted to constrain the rheology of oceanic lithosphere. Regardless of the assumed friction coefficient, the dry-olivine low-temperature plasticity flow laws of Goetze (1978), Evans & Goetze (1979), Raterron et al. (2004) and Mei et al. (2010) all provide quite a good fit to the observed Te at circum-Pacific subduction zones. This result contrasts with the Hawaiian Islands, where these flow laws are generally

  7. The effect of spatial truncation error on variance of gravity anomalies derived from inversion of satellite orbital and gradiometric data

    NASA Astrophysics Data System (ADS)

    Eshagh, Mehdi; Ghorbannia, Morteza

    2014-07-01

    The spatial truncation error (STE) is a significant systematic error in the integral inversion of satellite gradiometric and orbital data to gravity anomalies at sea level. In order to reduce the effect of STE, a larger area than the desired one is considered in the inversion process, but the anomalies located in its central part are selected as the final results. The STE influences the variance of the results as well because the residual vector, which is contaminated with STE, is used for its estimation. The situation is even more complicated in variance component estimation because of its iterative nature. In this paper, we present a strategy to reduce the effect of STE on the a posteriori variance factor and the variance components for inversion of satellite orbital and gradiometric data to gravity anomalies at sea level. The idea is to define two windowing matrices for reducing this error from the estimated residuals and anomalies. Our simulation studies over Fennoscandia show that the differences between the 0.5°×0.5° gravity anomalies obtained from orbital data and an existing gravity model have standard deviation (STD) and root mean squared error (RMSE) of 10.9 and 12.1 mGal, respectively, and those obtained from gradiometric data have 7.9 and 10.1 in the same units. In the case that they are combined using windowed variance components the STD and RMSE become 6.1 and 8.4 mGal. Also, the mean value of the estimated RMSE after using the windowed variances is in agreement with the RMSE of the differences between the estimated anomalies and those obtained from the gravity model.

  8. Detailed Gravity and Magnetic Survey of the Taylorsville Triassic Basin

    SciTech Connect

    Ali A. Nowroozi; John Leftwich

    1997-12-31

    Our research to date has involved the Interpretation of the Bouguer Gravity Anomaly Associated with the Richmond and Taylorsville Triassic Basins and its Vicinity. Continental rift basins around the world contain about 5% of the earth's sedimentary layers and produce about 20% of the total hydrocarbon production of the world (Ziegler (1983). Nearly 30 large basins of this type are reported by Manspeizer and Cousminer (1988) in eastern North America and northwestern Africa. There are eleven exposed basins of this type in the state of Virginia, from which nine are totally and two partially within the state's border. The number of unexposed basin's is not known. Exploration and drilling have been hampered largely because surface data are insufficient for even evaluation of those basins which are partly or completely exposed in the Piedmont Province. Generation of data through random exploratory drilling and seismic exploration is much too expensive and, therefore, these methods have not been widely used. In order to remedy this situation, we have used a geophysical method and completed a detailed and dense ground gravity surveys of the Richmond (Nowroozi and Wong, 1989, Daniels and Nowroozi, 1987). In this work we report our progress on collecting existing gravity data in a rectangular area covering the Richmond and Taylorsville Basins and its vicinity. The area covers one degree latitude and one degree longitude, starting at 37 North, 77 West and ending at 38 North, 78 West. Dr. David Daniels of the United State Geological Survey supplied us with more than 4900 Bouguer gravity anomalies in this area. The purpose of this progress report is to present the data in form of several maps and discuss its relation to the geology of the Triassic Basins and its vicinity. Johnson and others (1985) also presented a map of the Bouguer gravity anomaly of this area. However, their map covers a smaller area, and it is based on smaller number of observations.

  9. Spectral analysis of GEOS-3 altimeter data and frequency domain collocation. [to estimate gravity anomalies

    NASA Technical Reports Server (NTRS)

    Eren, K.

    1980-01-01

    The mathematical background in spectral analysis as applied to geodetic applications is summarized. The resolution (cut-off frequency) of the GEOS 3 altimeter data is examined by determining the shortest wavelength (corresponding to the cut-off frequency) recoverable. The data from some 18 profiles are used. The total power (variance) in the sea surface topography with respect to the reference ellipsoid as well as with respect to the GEM-9 surface is computed. A fast inversion algorithm for matrices of simple and block Toeplitz matrices and its application to least squares collocation is explained. This algorithm yields a considerable gain in computer time and storage in comparison with conventional least squares collocation. Frequency domain least squares collocation techniques are also introduced and applied to estimating gravity anomalies from GEOS 3 altimeter data. These techniques substantially reduce the computer time and requirements in storage associated with the conventional least squares collocation. Numerical examples given demonstrate the efficiency and speed of these techniques.

  10. Implications of the Utopia Gravity Anomaly for the Resurfacing of the Northern Plains of Mars

    NASA Technical Reports Server (NTRS)

    Banerdt, W. B.

    2004-01-01

    Whereas the surface units of the northern plain of Mars generally exhibit ages ranging from late Hesperian to Amazonian, interpretation of precise topographic measurements indicate that the age of the underlying "basement" is early Noachian, or almost as old as the southern highlands. This suggests that widespread but relatively superficial resurfacing has occurred throughout the northern plains since the end of early heavy bombardment. In this abstract I examine some of the possible implications of the subsurface structure inferred for the Utopia basin from gravity data on the nature of this resurfacing. The large, shallow, circular depression in Utopia Planitia has been identified as a huge impact basin, based on both geological evidence and detailed analysis of MOLA topography. Its diameter (approx. 3000 km) is equivalent to that of the Hellas basin, as is its inferred age (early Noachian). However, whereas Hellas is extremely deep with rough terrain and large slopes, the Utopia basin is a smooth, shallow, almost imperceptible bowl. Conversely, Utopia displays one of the largest (non-Tharsis-related) positive geoid anomalies on Mars, in contrast to a much more subdued negative anomaly over Hellas.

  11. Fluid/Gravity Correspondence, Second Order Transport and Gravitational Anomaly***

    NASA Astrophysics Data System (ADS)

    Megías, Eugenio; Pena-Benitez, Francisco

    2014-03-01

    We study the transport properties of a relativistic fluid affected by chiral and gauge-gravitational anomalies. The computation is performed in the framework of the fluid/gravity correspondence for a 5 dim holographic model with Chern-Simons terms in the action. We find new anomalous and non anomalous transport coefficients, as well as new contributions to the existing ones coming from the mixed gauge-gravitational anomaly. Consequences for the shear waves dispersion relation are analyzed. Talk given by E. Megías at the International Nuclear Physics Conference INPC 2013, 2-7 June 2013, Firenze, Italy.Supported by Plan Nacional de Altas Energías (FPA2009-07908, FPA2011-25948), Spanish MICINN Consolider-Ingenio 2010 Programme CPAN (CSD2007-00042), Comunidad de Madrid HEP-HACOS S2009/ESP-1473, Spanish MINECO's Centro de Excelencia Severo Ochoa Program (SEV-2012-0234, SEV-2012-0249), and the Juan de la Cierva Program.

  12. The mineralogy of global magnetic anomalies. [rock magnetic signatures and MAGSAT geological, and gravity correlations in West Africa

    NASA Technical Reports Server (NTRS)

    Haggerty, S. E. (Principal Investigator)

    1982-01-01

    Problems with the Curie balance, which severely hindered the acquisition of data, were rectified. Chemical analytical activities are proceeding satisfactorily. The magnetization characteristics of metamorphic suites were analyzed and susceptibility data for a wide range of metamorphic and igneous rocks. These rock magnetic signatures are discussed as well as the relationships between geology, gravity and MAGSAT anomalies of West Africa.

  13. Isostatic gravity map of the Monterey 30 x 60 minute quadrangle and adjacent areas, California

    USGS Publications Warehouse

    Langenheim, V.E.; Stiles, S.R.; Jachens, R.C.

    2002-01-01

    The digital dataset consists of one file (monterey_100k.iso) containing 2,385 gravity stations. The file, monterey_100k.iso, contains the principal facts of the gravity stations, with one point coded per line. The format of the data is described below. Each gravity station has a station name, location (latitude and longitude, NAD27 projection), elevation, and an observed gravity reading. The data are on the IGSN71 datum and the reference ellipsoid is the Geodetic Reference System 1967 (GRS67). The free-air gravity anomalies were calculated using standard formulas (Telford and others, 1976). The Bouguer, curvature, and terrain corrections were applied to the free-air anomaly at each station to determine the complete Bouguer gravity anomalies at a reduction density of 2.67 g/cc. An isostatic correction was then applied to remove the long-wavelength effect of deep crustal and/or upper mantle masses that isostatically support regional topography.

  14. An integrated airborne gravity survey of an offshore area near the northern Noto Peninsula, Japan

    NASA Astrophysics Data System (ADS)

    Komazawa, Masao; Okuma, Shigeo; Segawa, Jiro

    2010-02-01

    An airborne gravity survey using a helicopter was carried out in October 2008, offshore along the northern Noto Peninsula, to understand the shallow and regional underground structure. Eleven flight lines, including three tie lines, were arranged at 2km spacing within 20km of the coast. The total length of the flight lines was ~700km. The Bouguer anomalies computed from the airborne gravimetry are consistent with those computed from land and shipborne gravimetry, which gradually decrease in the offshore direction. So, the accuracy of the airborne system is considered to be adequate. A local gravity low in Wajima Bay, which was already known from seafloor gravimetry, was also observed. This suggests that the airborne system has a structural resolution of ~2km. Reduction of gravity data to a common datum was conducted by compiling the three kinds of gravity data, from airborne, shipborne, and land surveys. In the present study, we have used a solid angle numerical integration method and an iteration method. We finally calculated the gravity anomalies at 300m above sea level. We needed to add corrections of 2-5mGals in order to compile the airborne and shipborne gravity data smoothly, so the accuracy of the Bouguer anomaly map is considered to be nearly 2mGal on the whole, and 5mGals at worst in limited or local areas.

  15. Modelling the gravity and magnetic field anomalies of the Chicxulub crater

    NASA Technical Reports Server (NTRS)

    Aleman, C. Ortiz; Pilkington, M.; Hildebrand, A. R.; Roest, W. R.; Grieve, R. A. F.; Keating, P.

    1993-01-01

    The approximately 180-km-diameter Chicxulub crater lies buried by approximately 1 km of sediment on the northwestern corner of the Yucatan Peninsula, Mexico. Geophysical, stratigraphic and petrologic evidence support an impact origin for the structure and biostratigraphy suggests that a K/T age is possible for the impact. The crater's location is in agreement with constraints derived from proximal K/T impact-wave and ejecta deposits and its melt-rock is similar in composition to the K/T tektites. Radiometric dating of the melt rock reveals an age identical to that of the K/T tektites. The impact which produced the Chicxulub crater probably produced the K/T extinctions and understanding the now-buried crater will provide constraints on the impact's lethal effects. The outstanding preservation of the crater, the availability of detailed gravity and magnetic data sets, and the two-component target of carbonate/evaporites overlying silicate basement allow application of geophysical modeling techniques to explore the crater under most favorable circumstances. We have found that the main features of the gravity and magnetic field anomalies may be produced by the crater lithologies.

  16. Detection of Characteristic Precipitation Anomaly Patterns of El Nino / La Nina in Time- variable Gravity Fields by GRACE

    NASA Astrophysics Data System (ADS)

    Heki, K.; Morishita, Y.

    2007-12-01

    GRACE (Gravity Recovery and Climate Experiment) satellites, launched in March 2002, have been mapping monthly gravity fields of the Earth, allowing us to infer changes in surface mass, e.g. water and ice. Past findings include the ice mass loss in southern Greenland (Luthcke et al., 2006) and its acceleration in 2004 (Velicogna and Wahr, 2006), crustal dilatation by the 2004 Sumatra Earthquake (Han et al., 2006) and the postseismic movement of water in mantle (Ogawa and Heki, 2007). ENSO (El Nino and Southern Oscillation) brings about global climate impacts, together with its opposite phenomenon, La Nina. Ropelewski and Halpert (1987) showed typical precipitation patterns in ENSO years; characteristic regional-scale precipitation anomalies occur in India, tropical and southern Africa and South America. Nearly opposite precipitation anomalies are shown to occur in La Nina years (Ropelewski and Halpert, 1988). Here we report the detection of such precipitation anomaly patterns in the GRACE monthly gravity data 2002 - 2007, which includes both La Nina (2005 fall - 2006 spring) and El Nino (2006 fall - 2007 spring) periods. We modeled the worldwide gravity time series with constant trends and seasonal changes, and extracted deviations of gravity values at two time epochs, i.e. February 2006 and 2007, and converted them into the changes in equivalent surface water mass. East Africa showed negative gravity deviation (-20.5 cm in water) in 2006 February (La Nina), which reversed to positive (18.7 cm) in 2007 February (El Nino). Northern and southern parts of South America also showed similar see-saw patterns. Such patterns closely resemble to those found meteorologically (Ropelewski and Halpert, 1987; 1988), suggesting the potential of GRACE as a sensor of inter-annual precipitation anomalies through changes in continental water storage. We performed numerical simulations of soil moisture changes at grid points in land area incorporating the CMAP precipitation data, NCEP

  17. Principal facts for gravity stations in the Nevada portion of the Kingman 1 degree by 2 degree quadrangle

    NASA Astrophysics Data System (ADS)

    Bracken, R. E.; Kane, M. F.

    The principal facts contained in the tables of this report document 862 gravity stations in the Nevada portion of the Kingman 1 degree x 2 degree quadrangle. Two data sets are documented: 193 stations by the USGS, and 669 from the Department of Defense gravity data file. The description of the USGS stations includes gravity meter used, base station locations and values, elevation sources and errors, data reduction methods, and Bouguer anomaly error analysis. Only principal facts are listed for the Department of Defense data. All stations have been terrain corrected.

  18. The gravity anomaly field in the Gulf of Bothnia spatially characterized from satellite altimetry and in situ measurements

    NASA Astrophysics Data System (ADS)

    Noréus, J. P.; Nyborg, M. R.; Hayling, K. L.

    1997-06-01

    The gravity anomaly field in the Gulf of Bothnia has been investigated using (1) in situ high-precision measurements conducted on the sea ice during cold winters, and (2) gravity anomaly profiles computed from collinear satellite radar altimeter data from the Geosat ERM and the Topex/Poseidon missions. The in situ measurements were obtained from a collaboration between the Finnish Geodetic Institute, the Geological Survey of Sweden (SGU) and the National Survey of Sweden (LMV), and were processed with the geostatistical method called kriging. These data were used to calibrate the altimetric gravity. Altimetry generally resolves features of 20 km wavelength or longer, and in some cases detects shorter features when a sampling interval of 10 Hz is used. The precision of the along-track one-dimensional altimetric profiles corresponds to a gravity uncertainty of 2-3 mGal, and comparison with in situ measured gravity show 4 mGal discrepancy. The precision of the in situ measurements is better. However, depending on the sampling distance, the estimation uncertainty interior the in situ data areas may be up to 5 mGal between neighbouring data points. In regions with in situ data gaps, the estimation uncertainty of the in situ gravity measurements is rapidly increasing to a maximum of 9 mGal. An improved estimation uncertainty of 4-9 mGal was obtained in the same data gap regions with the support of satellite altimetry. Altimetric gravity is therefore used to estimate the gravity field in such regions, and to spatially characterize the gravity field in the Gulf of Bothnia.

  19. Estimation of regional mass anomalies from Gravity Recovery and Climate Experiment (GRACE) over Himalayan region

    NASA Astrophysics Data System (ADS)

    Agrawal, R.; Singh, S. K.; Rajawat, A. S.; Ajai

    2014-11-01

    Time-variable gravity changes are caused by a combination of postglacial rebound, redistribution of water and snow/ice on land and as well as in the ocean. The Gravity Recovery and Climate Experiment (GRACE) satellite mission, launched in 2002, provides monthly average of the spherical harmonic co-efficient. These spherical harmonic co-efficient describe earth's gravity field with a resolution of few hundred kilometers. Time-variability of gravity field represents the change in mass over regional level with accuracies in cm in terms of Water Equivalent Height (WEH). The WEH reflects the changes in the integrated vertically store water including snow cover, surface water, ground water and soil moisture at regional scale. GRACE data are also sensitive towards interior strain variation, surface uplift and surface subsidence cover over a large area. GRACE data was extracted over the three major Indian River basins, Indus, Ganga and Brahmaputra, in the Himalayas which are perennial source of fresh water throughout the year in Northern Indian Plain. Time series analysis of the GRACE data was carried out from 2003-2012 over the study area. Trends and amplitudes of the regional mass anomalies in the region were estimated using level 3 GRACE data product with a spatial resolution at 10 by 10 grid provided by Center for Space Research (CSR), University of Texas at Austin. Indus basin has shown a subtle decreasing trend from 2003-2012 however it was observed to be statistically insignificant at 95 % confidence level. Ganga and Brahmaputra basins have shown a clear decreasing trend in WEH which was also observed to be statistically significant. The trend analysis over Ganga and Brahamputra basins have shown an average annual change of -1.28 cm and -1.06 cm in terms of WEH whereas Indus basin has shown a slight annual change of -0.07 cm. This analysis will be helpful to understand the loss of mass in terms of WEH over Indian Himalayas and will be crucial for hydrological and

  20. A gravity model for the Coso geothermal area, California

    SciTech Connect

    Feighner, M.A.; Goldstein, N.E.

    1990-08-01

    Two- and three-dimensional gravity modeling was done using gridded Bouguer gravity data covering a 45 {times} 45 km region over the Coso geothermal area in an effort to identify features related to the heat source and to seek possible evidence for an underlying magma chamber. Isostatic and terrain corrected Bouguer gravity data for about 1300 gravity stations were obtained from the US Geological Survey. After the data were checked, the gravity values were gridded at 1 km centers for the area of interest centered on the Coso volcanic field. Most of the gravity variations can be explained by two lithologic units: (1) low density wedges of Quarternary alluvium with interbedded thin basalts (2.4 g/cm{sup 3}) filling the Rose Valley and Coso Basin/Indian Wells Valley, and (2) low density cover of Tertiary volcanic rocks and intercalated Coso Formation (2.49 g/cm{sup 3}). A 3-D iterative approach was used to find the thicknesses of both units. The gravity anomaly remaining after effects from Units 1 and 2 are removed is a broad north-south-trending low whose major peak lies 5 km north of Sugarloaf Mountain, the largest of the less than 0.3 m.y. old rhyolite domes in the Coso Range. Most of this residual anomaly can be accounted for by a deep, low-density (2.47 g/cm{sup 3}) prismatic body extending from 8 to about 30 km below the surface. While some of this anomaly might be associated with fractured Sierran granitic rocks, its close correlation to a low-velocity zone with comparable geometry suggests that the residual anomaly is probably caused a large zone of partial melt underlying the rhyolite domes of the Coso Range. 12 refs., 9 figs.

  1. Developing an optimally estimated earth gravity model to degree and order 360 from a global set of 30 deg x 30 deg mean surface gravity anomalies

    NASA Astrophysics Data System (ADS)

    Gleason, D. M.

    An optimally estimated earth gravity model (EGM), consisting of a set of geopotential coefficients through a maximum degree and order of 360, has been created from a global set of 259,200 30 deg by 30 deg surface mean gravity anomalies. The model is optimal in the sense that its derivation follows the principles of least-squares collocation which results in the coefficients' error variance/covariance matrix having a minimal trace value. This paper presents: (1) an overview of the mathematical and geodetic principles behind the construction of the model, (2) a discussion on the practical concerns and problems associated with the implementation of these principles on a present-day high speed computer, (3) a brief description of the global 30 deg input mean anomaly file used, (4) an analysis of the statistical properties of the coefficients and their accuracies, and (5) a prognosis for the future.

  2. Gravity-based Identification of Buried Craters with No Topographic Expression

    NASA Astrophysics Data System (ADS)

    Evans, A. J.; Zuber, M. T.

    2013-12-01

    With gravity data acquired by the dual Gravity Recovery and Interior Laboratory (GRAIL) spacecraft, in conjunction with altimetry data from the Lunar Orbiter Laser Altimeter (LOLA) investigation on the Lunar Reconnaissance Orbiter, we investigate buried craters within the lunar nearside maria. The contrast of low reflectance material of the lunar nearside maria against the high reflectance, anorthositic highlands' crust can be observed from Earth with the naked eye and is arguably one of the most recognizable features of the Moon. Geologic evidence supports the hypothesis that the maria flooded the lunar nearside between 3.8-2.5 Gya, obscuring much of the original physiographic expression of the nearside lowlands, nearly 20% of the entire surface. We use several approaches to visually identify quasi-circular mass anomalies (QCMAs) with minimal or no topographic expression in the free-air gravity and Bouguer anomaly. We identify these anomalies through a systematic search of the lunar nearside in the free-air gravity and Bouguer anomaly maps with shifted and stretched color-scale ranges. Additionally, to reduce identification bias of QCMAs with the largest gravity anomaly contrast and areal extent, we employ gravity gradiometry and antieigenvalues to enhance short-wavelength features in the gravity field. This approach provides a tool to simultaneously examine long- and short-wavelength structures without amplitude bias. Using these methods, we identify over 100 quasi-circular mass anomalies, likely to be ancient impact events, buried by the lunar maria. We use this crater population in conjunction with partially buried craters to investigate the average thickness, volume, and density of maria that have been emplaced on the lunar nearside.

  3. Middle proterozoic tectonic activity in west Texas and eastern New Mexico and analysis of gravity and magnetic anomalies

    SciTech Connect

    Adams, D.C.; Keller, G.R. )

    1994-03-01

    The Precambrian history of west Texas and eastern New Mexico is complex, consisting of four events: Early Proterozoic orogenic activity (16309-1800 Ma), formation of the western granite-rhyolite province (WGRP) (1340-1410 Ma), Grenville age tectonics (1116-1232 Ma), and middle Proterozoic extension possibly related to mid-continent rifting (1086-1109 Ma). Pre-Grenville tectonics, Grenville tectonics, and mid-continent rifting are represented in this area by the Abilene gravity minimum (AGM) and bimodal igneous rocks, which are probably younger. We have used gravity modeling and the comparison of gravity and magnetic anomalies with rock types reported from wells penetrating Precambrian basement to study the AGM and middle Proterozoic extension in this area. The AGM is an east-northeast-trending, 600 km long, gravity low, which extends from the Texas-Oklahoma border through the central basin platform (CBP) to the Delaware basin. This feature appears to predate formation of the mafic body in the CBP (1163 Ma) and is most likely related to Pre-Grenville tectonics, possibly representing a continental margin arc batholith. Evidence of middle Proterozoic extension is found in the form of igneous bodies in the CBP, the Van Horn uplift, the Franklin Mountains, and the Sacramento Mountains. Analysis of gravity and magnetic anomalies shows that paired gravity and magnetic highs are related to mafic intrusions in the upper crust. Mapping of middle Proterozoic igneous rocks and the paired anomalies outlines a 530 km diameter area of distributed east-west-oriented extension. The Debaca-Swisher terrain of shallow marine and clastic sedimentary rocks is age correlative with middle Proterozoic extension. These rocks may represent the lithology of possible Proterozoic exploration targets. Proterozoic structures were reactivated during the Paleozoic, affecting both the structure and deposition in the Permian basin.

  4. Multifractal singular value decomposition (MSVD) for extraction of marine gravity anomaly

    NASA Astrophysics Data System (ADS)

    LYU, Wenchao; Zhu, Benduo; Qiu, Yan

    2015-04-01

    The concept of singularity is used for characterizing different types of nonlinear natural processes, including volcanic eruptions, faults, cloud formation, landslides, rainfall, hurricanes, flooding, earthquakes, wildfires, oil fields and mineralization. The singularity often results in anomalous amounts of energy release or material accumulation within a narrow spatial-temporal interval.The marine gravitation field has multi-fractal features, which show different scale invariant properties in region and local field. The SVD can be used in geophysical data processing for signal and noise separation, radar processing for enhancing weak signals in vertical seismic profiles (VSP). It has also been used in multi component seismic polarization filters and evaluating the amount of wavy reflections in ground-penetrating radar (GPR) images of base surge deposits. With the SVD, a matrix X can be decomposed to a series of eigenvalues. The eigenvalues conformed fractal or multi-fractal distribution described with the power-law function. The multi-fractal SVD can be used for feature extraction and anomaly identification for marine gravity investigation.This paper aims to analyze the marine gravitation data using the SVD and multifractal methods. This paper will also aim to more clearly define the spatial relationship between marine mineralization and the deep geological structures in the field by extracting the marine gravitation information at a particular frequency to provide valuable in depth evidence for predicting new deposits and deep tectonic.

  5. Gravity and fault structures, Long Valley caldera, California

    SciTech Connect

    Carle, S.F.; Goldstein, N.E.

    1987-07-01

    The main and catastrophic phase of eruption in Long Valley occurred 0.73 m.y. ago with the eruption of over 600 km/sup 3/ of rhyolitic magma. Subsequent collapse of the roof rocks produced a caldera which is now elliptical in shape, 32 km east-west by 17 km north-south. The caldera, like other large Quarternary silicic ash-flow volcanoes that have been studied by various workers, has a nearly coincident Bouguer gravity low. Earlier interpretations of the gravity anomaly have attributed the entire anomaly to lower density rocks filling the collapsed structure. However, on the basis of many additional gravity stations and supporting subsurface data from several new holes, a much more complex and accurate picture has emerged of caldera structure. From a three-dimensional inversion of the residual Bouguer gravity data we can resolve discontinuities that seem to correlate with extensions of pre-caldera faults into the caldera and faults associated with the ring fracture. Some of these faults are believed related to the present-day hydrothermal upflow zone and the zone of youngest volcanic activity within the caldera.

  6. Underwater gravity meter survey of San Francisco and San Pablo bays, California, 1982

    USGS Publications Warehouse

    Childs, Jonathan R.; Beyer, L.A.; McCulloch, D.S.; McHendrie, G.A.; Steele, W.C.

    1983-01-01

    Seafloor gravity measurements were made at 281 bottom stations in San Francisco and San Pablo Bays, California, on a series of lines oriented approximately NNE.. Line spacing was approximately 2.8 km and stations along the lines mere spaced 0.5 to 1.5 km apart, between 0.5 and 1.5 km perpendicular to the axis. Sample Bouguer anomalies in the San Francisco Bay range from -15 to +15 mGals (?0.1 mgal), while anomalies in the San Pablo Bay are consistently negative, ranging from +4.0 to -40.0 mGal (?0.2 mGal).

  7. Determining the COB location along the Iberian margin and Galicia Bank from gravity anomaly inversion, residual depth anomaly and subsidence analysis

    NASA Astrophysics Data System (ADS)

    Cowie, Leanne; Kusznir, Nick; Manatschal, Gianreto

    2015-11-01

    Knowledge and understanding of the ocean-continent transition (OCT) structure, continent-ocean boundary (COB) location and crustal type are of critical importance in evaluating rifted continental margin formation and evolution. OCT structure, COB location and magmatic type also have important implications for the understanding of the geodynamics of continental breakup and in the evaluation of petroleum systems in deep-water frontier oil and gas exploration at rifted continental margins. Mapping the distribution of thinned continental crust and lithosphere, its distal extent and the start of unequivocal oceanic crust and hence determining the OCT structure and COB location at rifted continental margins is therefore a generic global problem. In order to assist in the determination of the OCT structure and COB location, we present methodologies using gravity anomaly inversion, residual depth anomaly (RDA) analysis and subsidence analysis, which we apply to the west Iberian rifted continental margin. The west Iberian margin has one of the most complete data sets available for deep magma-poor rifted margins, so there is abundant data to which the results can be calibrated. Gravity anomaly inversion has been used to determine Moho depth, crustal basement thickness and continental lithosphere thinning; subsidence analysis has been used to determine the distribution of continental lithosphere thinning; and RDAs have been used to investigate the OCT bathymetric anomalies with respect to expected oceanic bathymetries at rifted continental margins. These quantitative analytical techniques have been applied to the west Iberian rifted continental margin along profiles IAM9, Lusigal 12 (with the TGS-extension) and ISE-01. Our predictions of OCT structure, COB location and magmatic type (i.e. the volume of magmatic addition, whether the margin is `normal' magmatic, magma-starved or magma-rich) have been tested and validated using ODP wells (Legs 103, 149 and 173), which provide

  8. The use of the WGM2012 gravity model to acquire gravimetric data necessary for the reduction of geodetic observations

    NASA Astrophysics Data System (ADS)

    Olszak, Tomasz; Barlik, Marcin

    2014-05-01

    World Gravity Model WGM2012 is the first release of high resolution description inter alia Bouguer and free-air gravity anomaly. It has been created by the Bureau Gravimétrique International (BGI) on base of EGM2008 geopotential model and high resolution topographic model. The poster provides an assessment of the WGM2012 gravity data sources for use in the reduction of geodetic observations. For reductions of geodetic observations onto geoid and ellipsoid (eg. astronomical coordinates, deflections of the vertical, astronomical azimuth and linear measurements) it is necessary a knowledge of the gravity field parameters. Also, in the leveling network it is necessary to collect such information to calculate the normal (or orthometric) correction. The study compared terrestrial data from the Polish National Geological Institute including anomalies and data from the WGM2012 model in the context of using model gravity data to issues related to geodesic reductions.

  9. Crustal structure under the central High Atlas Mountains (Morocco) from geological and gravity data

    NASA Astrophysics Data System (ADS)

    Ayarza, P.; Alvarez-Lobato, F.; Teixell, A.; Arboleya, M. L.; Tesón, E.; Julivert, M.; Charroud, M.

    2005-05-01

    Seismic wide angle and receiver function results together with geological data have been used as constraints to build a gravity-based crustal model of the central High Atlas of Morocco. Integration of a newly acquired set of gravity values with public data allowed us to undertake 2-2.5D gravity modelling along two profiles that cross the entire mountain chain. Modelling suggests moderate crustal thickening, and a general state of Airy isostatic undercompensation. Localized thickening appears restricted to the vicinity of a north-dipping crustal-scale thrust fault, that offsets the Moho discontinuity and defines a small crustal root which accounts for the minimum Bouguer gravity anomaly values. Gravity modelling indicates that this root has a northeasterly strike, slightly oblique to the ENE general orientation of the High Atlas belt. A consequence of the obliquity between the High Atlas borders and its internal and deep structure is the lack of correlation between Bouguer gravity anomaly values and topography. Active buckling affecting the crust, a highly elevated asthenosphere, or a combination of both are addressed as side mechanisms that help to maintain the high elevations of the Atlas mountains.

  10. Evaluation of low-temperature geothermal potential in Utah and Goshen Valleys and adjacent areas, Utah. Part I. Gravity survey

    SciTech Connect

    Davis, D.A.; Cook, K.L.

    1983-04-01

    During 1980 and 1981 a total of 569 new gravity stations were taken in Utah and Goshen Valleys and adjacent areas, Utah. The new stations were combined with 530 other gravity stations taken in previous surveys which resulted in a compilation of 1099 stations which were used in this study. The additional surveys were undertaken to assist in the evaluation of the area for the possible development of geothermal resources by providing an interpreted structural framework by delineating faults, structural trends, intrusions, thickness of valley fill, and increased density of host rock. The gravity data are presented as (1) a complete Bouguer gravity anomaly map with a 2 mgal contour interval on a scale of 1:100,000 and (2) five generally east-trending gravity profiles. A geologic interpretation of the study area was made from the gravity map and from the interpretive geologic cross sections which were modeled along the gravity profiles.

  11. Evidence for Topographic Swells Beneath Gravity Lineations in the South Pacific.

    NASA Astrophysics Data System (ADS)

    Harmon, N.; Forsyth, D. W.; Scheirer, D.

    2004-12-01

    The Gravity Lineations Intraplate Melting Petrologic and Seismologic Expedition (GLIMPSE) experiment is investigating the origins of the gravity lineations in the South Pacific and their relationship to intraplate volcanism at the Sojourn and Hotu Matua ridge systems. Using the satellite free air gravity anomaly and high quality shipboard bathymetry in the GLIMPSE study region, we have calculated the Mantle Bouguer Anomaly (MBA) and the residual Mantle Bouguer Anomaly (rMBA). In the MBA, we see strong negative anomalies (~20-40 mGals) beneath the Sojourn and Brown Ridges as well as beneath the Hotu Matua volcanic complex, indicating low-density material beneath the ridge systems in the form of thickened crust or lower density mantle material. We subtract the effects of surface loading of an elastic plate by the volcanic ridges to find the residual topography and the residual MBA. The residual seafloor topography shows a systematic ~200 km wavelength undulation in the seafloor with a strike roughly parallel to the spreading direction, producing residual bathymetric highs of 100-300 m beneath the Sojourn and Hotu Matua ridge systems. There are broad (100 km wide) negative anomaly bands in the rMBA of ~10-40 mGals beneath the entire length of the Sojourn Ridge to the East Pacific Rise and discontinuously from west of Hotu Matua to the EPR. Similar features are found in the extension of the Puka Puka ridge into the Rano Rahi seamount field. The swells beneath the intraplate volcanism and the gravity lineations require a contribution from subsurface positively buoyant low-density material. The seismic refraction and Rayleigh wave dispersion experiments corroborate the existence of anomalies at depth. The swells contradict lithospheric cracking models of the formation of the gravity lineations that predict the gravity lineations should be located over bathymetric troughs, and favor dynamic models such as small-scale convection.

  12. A New Search for Lunar Mascon Basins using Detrended Kaguya (SELENE) Gravity: Implications for GRAIL

    NASA Astrophysics Data System (ADS)

    Dombard, A. J.; Hauck, S. A.; Balcerski, J.

    2012-12-01

    The collection of GRAIL data and imminent release of its first gravity models will revolutionize understanding of the lunar interior, which motivates an assessment of the current state of knowledge. A primary goal of the GRAIL mission is to understand better mascon basins, large impact craters that display significant positive free-air and Bouguer gravity anomalies. Discovered in a handful of nearside basins during preparations for the Apollo landings and recently expanded by the global Kaguya (SELENE) gravity models, an important question is why is not every large crater a mascon basin, as less than half of the 41 impact basins > 300 km in diameter (minus South Pole-Aitken) have been previously determined to be mascons. An issue not generally considered in the identification of mascons is that the topography, and hence Bouguer gravity, display long-wavelength regional signals that might mask some mascons. Here, we use the SGM100i Kaguya gravity model and LRO's LOLA shape model to examine the free-air, topographic (arising solely from topography), and Bouguer gravity, detrended by omitting the first 5 spherical harmonic degrees from our expansions. In contrast to past studies, we find that most large basins (28 of 41) display characteristics of mascons (e.g., a strong positive Bouguer anomaly generally narrower than the surface rim). Negative annuli surrounding the central highs in the free-air gravity do not exist in the Bouguer gravity, with only 2 definitive exceptions. The fact that the majority of the Bouguer anomalies are narrower than the basin rim and that the negative free-air annulus appears to be a product of the surface topography has implications for the formation of the basins. We propose that beneath a forming large basin, the mantle uplifts in response to the large isostatic imbalance with the transient crater, while the surface topography forms from not only upward but inward collapse of the transient crater's rim wall and adjustment of the melt

  13. Calculation of geoid undulations and gravity anomalies in the South China Sea by using the TOPEX/Poseidon and Geosat altimeter data

    NASA Astrophysics Data System (ADS)

    Zhang, Youguang; Zhang, Jie; Ji, Yonggang; Zhang, Huiqin

    2003-05-01

    In this paper, using TOPEX/Poseidon (9~346cycle) and Geosat/ERM(1~60cycle) altimeter data, the author applies combined adjustment model for calculating the South China Sea geoid undulations after data preprocessing. The difference between calculation result and OSU91A model is 30cm (spatial resolution is 22km). In addition, 12"x12" South China Sea gravity anomalies are calculated by using above geoid data and improved Stokes inverse formula. Contrasted with Scripps Institution of Oceanography gravity anomalies data, the accuracy of computation of gravity anomalies is 12´x10-5m/s2. These computations show that calculation speed is fast and calculation efficiency is high, so the method can calculate rapidly gravity anomalies in special sea area.

  14. Constraints on timing and magnitude of early global expansion of the Moon from topographic features in linear gravity anomaly areas

    NASA Astrophysics Data System (ADS)

    Sawada, Natsuki; Morota, Tomokatsu; Kato, Shinsuke; Ishihara, Yoshiaki; Hiramatsu, Yoshihiro

    2016-05-01

    Gravity data obtained from the Gravity Recovery and Interior Laboratory have revealed linear gravity anomalies (LGAs) formed by the early global expansion of the Moon and subsequent magma intrusion. In this study, using Lunar Orbiter Laser Altimeter topographic data, we investigated topographic profiles across LGAs to verify that they were formed by extensional tectonics. We found that 17 of the 20 LGAs investigated exhibited a valley structure, suggesting that they were formed by tensile stress. Assuming that these topographic depressions accompanied graben formation, the increase in the lunar radius is estimated to be on the order of several tens of meters. On the other hand, assuming that these topographic depressions accompanied flexure of elastic lithosphere due to the LGA load, the elastic thickness during the LGA formation is estimated as ~10 km. The crater frequencies in the vicinity of LGAs indicate that the peak tectonic activity occurred before the basin-forming epoch.

  15. Mean gravity anomalies from a combination of Apollo/ATS 6 and GEOS 3/ATS 6 SST tracking campaigns. [Satellite to Satellite Tracking

    NASA Technical Reports Server (NTRS)

    Kahn, W. D.; Klosko, S. M.; Wells, W. T.

    1982-01-01

    Advances in satellite tracking data accuracy and coverage over the past 15 years have led to major improvements in global geopotential models. But the spacial resolution of the gravity field obtained solely from satellite dynamics sensed by tracking data is still of the order of 1000 km. Attention is given to an approach which will provide information regarding the fine structure of the gravity field on the basis of an application of local corrections to the global field. According to this approach, a basic satellite to satellite tracked (SST) range-rate measurement is constructed from the link between a ground station, a geosynchronous satellite (ATS 6), and a near-earth satellite (Apollo or GEOS 3). Attention is given to a mathematical model, the simulation of SST gravity anomaly estimation accuracies, a gravity anomaly estimation from GEOS 3/ATS 6 and Apollo/ATS 6 SST observations, and an evaluation of the mean gravity anomalies determined from SST.

  16. Gravity measurements in the vicinity of Georges Bank

    USGS Publications Warehouse

    Hendricks, John D.; Robb, James D.

    1973-01-01

    A total of 97 new bottom gravity measurements on the continental shelf in the vicinity of Georges Bank was reduced to the simple Bouguer anomaly, using a density of 2.80 gm per cm3 for the correction. Results help substantiate the presence of mafic and felsic intrusive bodies along the northern edge of the bank. A gravity low near the center of the bank, trending northeast, corresponds to the Georges Bank trough. An abrupt change in the gravity gradient near the southeast edge of the bank probably represents the thinning of the crust from continental to oceanic thicknesses. Differences in gravity gradient support the suggestion of a fault along the northern edge of the bank.

  17. Lunar impact basins revealed by Gravity Recovery and Interior Laboratory measurements.

    PubMed

    Neumann, Gregory A; Zuber, Maria T; Wieczorek, Mark A; Head, James W; Baker, David M H; Solomon, Sean C; Smith, David E; Lemoine, Frank G; Mazarico, Erwan; Sabaka, Terence J; Goossens, Sander J; Melosh, H Jay; Phillips, Roger J; Asmar, Sami W; Konopliv, Alexander S; Williams, James G; Sori, Michael M; Soderblom, Jason M; Miljković, Katarina; Andrews-Hanna, Jeffrey C; Nimmo, Francis; Kiefer, Walter S

    2015-10-01

    Observations from the Gravity Recovery and Interior Laboratory (GRAIL) mission indicate a marked change in the gravitational signature of lunar impact structures at the morphological transition, with increasing diameter, from complex craters to peak-ring basins. At crater diameters larger than ~200 km, a central positive Bouguer anomaly is seen within the innermost peak ring, and an annular negative Bouguer anomaly extends outward from this ring to the outer topographic rim crest. These observations demonstrate that basin-forming impacts remove crustal materials from within the peak ring and thicken the crust between the peak ring and the outer rim crest. A correlation between the diameter of the central Bouguer gravity high and the outer topographic ring diameter for well-preserved basins enables the identification and characterization of basins for which topographic signatures have been obscured by superposed cratering and volcanism. The GRAIL inventory of lunar basins improves upon earlier lists that differed in their totals by more than a factor of 2. The size-frequency distributions of basins on the nearside and farside hemispheres of the Moon differ substantially; the nearside hosts more basins larger than 350 km in diameter, whereas the farside has more smaller basins. Hemispherical differences in target properties, including temperature and porosity, are likely to have contributed to these different distributions. Better understanding of the factors that control basin size will help to constrain models of the original impactor population. PMID:26601317

  18. Lunar impact basins revealed by Gravity Recovery and Interior Laboratory measurements

    PubMed Central

    Neumann, Gregory A.; Zuber, Maria T.; Wieczorek, Mark A.; Head, James W.; Baker, David M. H.; Solomon, Sean C.; Smith, David E.; Lemoine, Frank G.; Mazarico, Erwan; Sabaka, Terence J.; Goossens, Sander J.; Melosh, H. Jay; Phillips, Roger J.; Asmar, Sami W.; Konopliv, Alexander S.; Williams, James G.; Sori, Michael M.; Soderblom, Jason M.; Miljković, Katarina; Andrews-Hanna, Jeffrey C.; Nimmo, Francis; Kiefer, Walter S.

    2015-01-01

    Observations from the Gravity Recovery and Interior Laboratory (GRAIL) mission indicate a marked change in the gravitational signature of lunar impact structures at the morphological transition, with increasing diameter, from complex craters to peak-ring basins. At crater diameters larger than ~200 km, a central positive Bouguer anomaly is seen within the innermost peak ring, and an annular negative Bouguer anomaly extends outward from this ring to the outer topographic rim crest. These observations demonstrate that basin-forming impacts remove crustal materials from within the peak ring and thicken the crust between the peak ring and the outer rim crest. A correlation between the diameter of the central Bouguer gravity high and the outer topographic ring diameter for well-preserved basins enables the identification and characterization of basins for which topographic signatures have been obscured by superposed cratering and volcanism. The GRAIL inventory of lunar basins improves upon earlier lists that differed in their totals by more than a factor of 2. The size-frequency distributions of basins on the nearside and farside hemispheres of the Moon differ substantially; the nearside hosts more basins larger than 350 km in diameter, whereas the farside has more smaller basins. Hemispherical differences in target properties, including temperature and porosity, are likely to have contributed to these different distributions. Better understanding of the factors that control basin size will help to constrain models of the original impactor population. PMID:26601317

  19. Validation of GOCE global gravitational field models by comparison with regional geoid and gravity anomaly surfaces

    NASA Astrophysics Data System (ADS)

    Sprlak, M.; Gerlach, C.; Pettersen, B. R.; Omang, O. C. D.

    2012-04-01

    , the most accurate filtering procedure is applied in validation of real GOCE models. The validation experiment is performed with respect to gravity anomalies and geoid undulations over the territory of Scandinavia.

  20. Gravity anomalies, crustal structure, and seismicity at subduction zones: 1. Seafloor roughness and subducting relief

    NASA Astrophysics Data System (ADS)

    Bassett, Dan; Watts, Anthony B.

    2015-05-01

    An ensemble averaging technique is used to remove the long-wavelength topography and gravity field from subduction zones. >200 residual bathymetric and gravimetric anomalies are interpreted within fore arcs, many of which are attributed to the tectonic structure of the subducting plate. The residual-gravimetric expression of subducting fracture zones extends >200 km landward of the trench axis. The bathymetric expression of subducting seamounts with height ≥1 km and area ≥500 km2 (N=36), and aseismic ridges (N>10), is largest near the trench (within 70 km) and above shallow subducting slab depths (SLAB1.0 <17 km). Subducting seamounts are similar in wavelength, amplitude, and morphology to unsubducted seamounts. Morphology, spatial distributions, and reduced levels of seismicity are considered inconsistent with mechanical models proposing wholesale decapitation, and the association of subducting seamounts with large-earthquakes. Subducting aseismic ridges are associated with uplift and steepening of the outer fore arc, a gradual reduction in residual bathymetric expression across the inner fore arc, and a local increase in the width and elevation of the volcanic-arc/orogen. These contrasting expressions reflect the influence of margin-normal variations in rigidity on where and how the upper plate deforms, both to accommodate subducting relief and in response to stresses transmitted across the plate interface. The outer fore arc and arc have lower rigidity due to fracturing and thermal weakening, respectively. Similar associations with complex earthquakes and fault creep suggest aseismic ridge subduction may also be accommodated by the development and evolution of a broad fracture network, the geometrical strength of which may exceed the locking strength of a smooth fault.

  1. Integrating stations from the North America Gravity Database into a local GPS-based land gravity survey

    USGS Publications Warehouse

    Shoberg, Thomas G.; Stoddard, Paul R.

    2013-01-01

    The ability to augment local gravity surveys with additional gravity stations from easily accessible national databases can greatly increase the areal coverage and spatial resolution of a survey. It is, however, necessary to integrate such data seamlessly with the local survey. One challenge to overcome in integrating data from national databases is that these data are typically of unknown quality. This study presents a procedure for the evaluation and seamless integration of gravity data of unknown quality from a national database with data from a local Global Positioning System (GPS)-based survey. The starting components include the latitude, longitude, elevation and observed gravity at each station location. Interpolated surfaces of the complete Bouguer anomaly are used as a means of quality control and comparison. The result is an integrated dataset of varying quality with many stations having GPS accuracy and other reliable stations of unknown origin, yielding a wider coverage and greater spatial resolution than either survey alone.

  2. Complete Bouguer gravity map of the Medicine Lake Quadrangle, California

    USGS Publications Warehouse

    Finn, C.

    1981-01-01

    A mathematical technique, called kriging, was programmed for a computer to interpolate hydrologic data based on a network of measured values in west-central Kansas. The computer program generated estimated values at the center of each 1-mile section in the Western Kansas Groundwater Management District No. 1 and facilitated contouring of selected values that are needed in the effective management of ground water for irrigation. The kriging technique produced objective and reproducible maps that illustrated hydrologic conditions in the Ogallala aquifer, the principal source of water in west-central Kansas. Maps of the aquifer, which use a 3-year average, included the 1978-80 water-table altitudes, which ranged from about 2,580 to 3,720 feet; the 1978-80 saturated thicknesses, which ranged from about 0 to 250 feet; and the percentage changes in saturated thickness from 1950 to 1978-80, which ranged from about a 50-percent increase to a 100-percent decrease. A map showing errors of estimate also was provided as a measure of reliability for the 1978-80 water-table altitudes. Errors of estimate ranged from 2 to 24 feet. (USGS)

  3. Model parameter estimations from residual gravity anomalies due to simple-shaped sources using Differential Evolution Algorithm

    NASA Astrophysics Data System (ADS)

    Ekinci, Yunus Levent; Balkaya, Çağlayan; Göktürkler, Gökhan; Turan, Seçil

    2016-06-01

    An efficient approach to estimate model parameters from residual gravity data based on differential evolution (DE), a stochastic vector-based metaheuristic algorithm, has been presented. We have showed the applicability and effectiveness of this algorithm on both synthetic and field anomalies. According to our knowledge, this is a first attempt of applying DE for the parameter estimations of residual gravity anomalies due to isolated causative sources embedded in the subsurface. The model parameters dealt with here are the amplitude coefficient (A), the depth and exact origin of causative source (zo and xo, respectively) and the shape factors (q and ƞ). The error energy maps generated for some parameter pairs have successfully revealed the nature of the parameter estimation problem under consideration. Noise-free and noisy synthetic single gravity anomalies have been evaluated with success via DE/best/1/bin, which is a widely used strategy in DE. Additionally some complicated gravity anomalies caused by multiple source bodies have been considered, and the results obtained have showed the efficiency of the algorithm. Then using the strategy applied in synthetic examples some field anomalies observed for various mineral explorations such as a chromite deposit (Camaguey district, Cuba), a manganese deposit (Nagpur, India) and a base metal sulphide deposit (Quebec, Canada) have been considered to estimate the model parameters of the ore bodies. Applications have exhibited that the obtained results such as the depths and shapes of the ore bodies are quite consistent with those published in the literature. Uncertainty in the solutions obtained from DE algorithm has been also investigated by Metropolis-Hastings (M-H) sampling algorithm based on simulated annealing without cooling schedule. Based on the resulting histogram reconstructions of both synthetic and field data examples the algorithm has provided reliable parameter estimations being within the sampling limits of

  4. Regional gravity and magnetic anomalies related to a Proterozoic carbonatite terrane in the eastern Mojave Desert, California

    NASA Astrophysics Data System (ADS)

    Denton, K. M.; Ponce, D. A.; Miller, D. M.; Jernigan, C. T.

    2014-12-01

    One of the world's largest rare earth element carbonatite deposits is located at Mountain Pass in the eastern Mojave Desert, California. The 1.4 Ga carbonatite deposit is hosted by and intruded into 1.7 Ga gneiss and schist that occurs in a narrow north-northwest trending belt along the eastern parts of Clark Mountain Range, Mescal Range, and Ivanpah Mountains. The carbonatite is associated with an ultrapotassic intrusive suite that ranges from shonkinite through syenite and granite. Regional geophysical data reveal that the eastern Mojave carbonatite terrane occurs along the northeast edge of a prominent magnetic high and the western margin of a gravity high along the eastern Clark Mountain Range. To improve our understanding of the geophysical and structural framework of the eastern Mojave carbonatite terrane, we collected over 1900 gravity stations and over 600 physical rock property samples to augment existing geophysical data. Carbonatite intrusions typically have distinct gravity, magnetic, and radiometric signatures because these deposits are relatively dense, contain magnetite, and are enriched in thorium or uranium. However, our results show that the carbonatite is essentially nonmagnetic with an average susceptibility of 0.18 x 10-3 SI (n=31) and the associated ultrapotassic intrusive suite is very weakly magnetic with an average susceptibility of 2.0 x 10-3 SI (n=36). Although the carbonatite body is nonmagnetic, it occurs along a steep gradient of a prominent aeromagnetic anomaly. This anomaly may reflect moderately magnetic mafic intrusive rocks at depth. East of the ultrapotassic intrusive rocks, a prominent north trending magnetic anomaly occurs in the central part of Ivanpah Valley. Based on geologic mapping in the Ivanpah Mountains, this magnetic anomaly may reflect Paleoproterozoic mafic intrusive rocks related to the 1.7 Ga Ivanpah Orogeny. Physical property measurements indicate that exposed amphibolite along the eastern Ivanpah Mountains are

  5. Frozen subduction in the Yangtze block: insights from the deep seismic profiling and gravity anomaly in east Sichuan fold belt

    NASA Astrophysics Data System (ADS)

    Xiong, Xiaosong; Gao, Rui; Wang, Haiyan; Zhang, Jisheng; Guo, Lianghui

    2016-04-01

    The Sichuan basin is the main part of the middle-upper Yangtze block, which has been experienced a long-term tectonic evolution since Archean. The Yangtze block was regarded as a stable block until the collision with the Cathaysia block in late Neoproterozoic. A new deep seismic reflection profile conducted in the eastern Sichuan fold belt (ESFB) discovered a serials of south-dipping reflectors shown from lower crust to the mantle imply a frozen subduction zone within the Yangtze block. In order to prove the speculation, we also obtain the middle-lower crustal gravity anomalies by removing the gravity anomalies induced by the sedimentary rocks and the mantle beneath the Moho, which shows the mid-lower crustal structure of the Sichuan basin can be divided into eastern and western parts. Combined with the geochronology and Aeromagnetic anomalies, we speculated the Yangtze block was amalgamated by the West Sichuan and East Sichuan blocks separated by the Huayin-Chongqing line. The frozen subduction zone subsequently shifted to a shear zone accommodated the lower crustal shortening when the decollement at the base of the Nanhua system functioned in the upper plate.

  6. Integrated Analysis on Gravity and Magnetic Fields of the Hailar Basin, NE China: Implications for Basement Structure and Deep Tectonics

    NASA Astrophysics Data System (ADS)

    Sun, B.; Wang, L.; Dong, P.; Scientific Team Of Applied Geophysics

    2010-12-01

    The Hailar Basin is one of the most representative basins among the Northeast China Basin Group, which is situated in the east of East Asia Orogene between the Siberia Plate and the North China Plate. Based on the detailed analysis of the Bouguer gravity anomaly, aeromagnetic anomaly as well as petrophysical data, we studied the features of gravity-magnetic fields in the basin and its neighboring areas. A combined approach of Wavelet Multi-scale Decomposition and Power Spectrum Analysis was adopted to quantitatively grade the gravity and magnetic anomalies into four levels. Accordingly, the apparent depths of the source fields can be assessed. The results reveal the crustal density and magnetic structures of the Hailar Basin. Low-order wavelet details of gravity-magnetic anomalies were carried out on studying basin basement structure. Seven major basement faults of the basin were identified, and the basement lithology was discussed and predicted. Three major uplifts and 14 depressions were delineated according to basement depth inversion by the Park method. High-order wavelet approximations of gravity-magnetic anomalies were carried out on studying deep tectonics of the basin. The average Moho depth of the study area is about 40 km, with a mantle uplift located in the northeast of the basin. The average depth of the Curie interface is about 19 km, while the uplift of the Curie interface is in the basin center and its east and west sides are depressions. Finally, inversion of Bouguer gravity anomalies was conducted on an across-basin GGT profile using the Wavelet Multi-scale Decomposition. The inversion results are consistent with those of GGT seismic inversion, suggesting that the Wavelet Multi-scale Decomposition can be applied to distinguish major crustal density interfaces.

  7. Gravity anomaly and geoid undulation results in local areas from GEOS-3 altimeter data

    NASA Technical Reports Server (NTRS)

    Rapp, R. H.

    1979-01-01

    The adjusted GEOS-3 altimeter data, taken as averages within a data frame, have been used to construct free air anomaly and geoid undulation profiles and maps in areas of geophysical interest. Profiles were constructed across the Philippine Trench (at a latitude of 6 deg) and across the Bonin Trench (at a latitude of 28 deg). In the latter case an anomaly variation of 443 mgals in 143 km was derived from the altimeter data. These variations agreed reasonably with terrestrial estimates, considering the predicted point accuracy was about + or - 27 mgals. An area over the Patton Sea mounts was also investigated with the altimeter anomaly field agreeing well with the terrestrial data except for the point directly over the top of the sea mount. It is concluded that the GEOS-3 altimeter data is valuable not only for determining 5 deg and 1 deg x 1 deg mean anomalies, but also can be used to describe more local anomaly variations.

  8. The determination of gravity anomalies from geoid heights using the inverse Stokes' formula, Fourier transforms, and least squares collocation

    NASA Technical Reports Server (NTRS)

    Rummel, R.; Sjoeberg, L.; Rapp, R. H.

    1978-01-01

    A numerical method for the determination of gravity anomalies from geoid heights is described using the inverse Stokes formula. This discrete form of the inverse Stokes formula applies a numerical integration over the azimuth and an integration over a cubic interpolatory spline function which approximates the step function obtained from the numerical integration. The main disadvantage of the procedure is the lack of a reliable error measure. The method was applied on geoid heights derived from GEOS-3 altimeter measurements in the calibration area of the GEOS-3 satellite.

  9. Gravity anomalies, crustal structure, and seismicity at subduction zones: 2. Interrelationships between fore-arc structure and seismogenic behavior

    NASA Astrophysics Data System (ADS)

    Bassett, Dan; Watts, Anthony B.

    2015-05-01

    An ensemble-averaging technique is used to remove the long-wavelength topography and gravity field associated with subduction zones. Short-wavelength residual anomalies are attributed to the tectonic structure of subducting and overthrusting plates. A paired (positive-negative) fore-arc anomaly is observed consisting of a long (>1000 km), linear, trench-parallel ridge landward of the deep-sea-terrace basin. Ridges have amplitudes of 1500-3000 m and 160-240 mGal, wavelengths of 150-200 km, and high gravity anomaly to topography ratios (50-75 mGal km-1). The ridge crests correlate with the downdip limit of coseismic slip and strong interplate coupling and in Cascadia, the updip limit of tremor epicenters. The ridge crest may be interpreted as defining the boundary between the velocity-weakening and seismogenic region of the subduction interface and the downdip frictional transition zone. In Tonga-Kermadec, the Kuril Islands and Chile landward ridges are associated with extinct volcanic arcs. Paired anomalies are attributed to the preferential subduction erosion of the outer fore arc and a spatially varying combination of (a) lower crustal underplating beneath the inner fore arc, (b) the transformation of interseismic strain into permanent geologic strain via faulting, folding, or buckling of the inner fore arc, and (c) the relative trenchward migration of extinct volcanic arcs in regions operating with a net crustal deficit. Along-strike transitions in fore-arc morphology and seismogenic behavior are related to preexisting crustal structure of subducting and overthrusting plates. Fore arcs have the added potential of recording the time-integrated response of the upper plate to subduction processes, and fore-arc structure should be considered in tandem with seismological observations.

  10. The Wallula fault and tectonic framework of south-central Washington, as interpreted from magnetic and gravity anomalies

    NASA Astrophysics Data System (ADS)

    Blakely, Richard J.; Sherrod, Brian L.; Weaver, Craig S.; Wells, Ray E.; Rohay, Alan C.

    2014-06-01

    The Yakima fold and thrust belt (YFTB) in central Washington has accommodated regional, mostly north-directed, deformation of the Cascadia backarc since prior to emplacement of Miocene flood basalt of the Columbia River Basalt Group (CRBG). The YFTB consists of two structural domains. Northern folds of the YFTB strike eastward and terminate at the western margin of a 20-mGal negative gravity anomaly, the Pasco gravity low, straddling the North American continental margin. Southern folds of the YFTB strike southeastward, form part of the Olympic-Wallowa lineament (OWL), and pass south of the Pasco gravity low as the Wallula fault zone. An upper crustal model based on gravity and magnetic anomalies suggests that the Pasco gravity low is caused in part by an 8-km-deep Tertiary basin, the Pasco sub-basin, abutting the continental margin and concealed beneath CRBG. The Pasco sub-basin is crossed by north-northwest-striking magnetic anomalies caused by dikes of the 8.5 Ma Ice Harbor Member of the CRBG. At their northern end, dikes connect with the eastern terminus of the Saddle Mountains thrust of the YFTB. At their southern end, dikes are disrupted by the Wallula fault zone. The episode of NE-SW extension that promoted Ice Harbor dike injection apparently involved strike-slip displacement on the Saddle Mountains and Wallula faults. The amount of lateral shear on the OWL impacts the level of seismic hazard in the Cascadia region. Ice Harbor dikes, as mapped with aeromagnetic data, are dextrally offset by the Wallula fault zone a total of 6.9 km. Assuming that dike offsets are tectonic in origin, the Wallula fault zone has experienced an average dextral shear of 0.8 mm/y since dike emplacement 8.5 Ma, consistent with right-lateral stream offsets observed at other locations along the OWL. Southeastward, the Wallula fault transfers strain to the north-striking Hite fault, the possible location of the M 5.7 Milton-Freewater earthquake in 1936.

  11. Analyzing the Broken Ridge area of the Indian Ocean using magnetic and gravity anomaly maps and geoid undulation and bathymetry data

    NASA Technical Reports Server (NTRS)

    Lazarewicz, A. R.; Sailor, R. V. (Principal Investigator)

    1982-01-01

    A higher resolution anomaly map of the Broken Ridge area (2 degree dipole spacing) was produced and reduced to the pole using quiet time data for this area. The map was compared with equally scaled maps of gravity anomaly, geoid undulation, and bathymetry. The ESMAP results were compared with a NASA MAGSAT map derived by averaging data in two-degree bins. A survey simulation was developed to model the accuracy of MAGSAT anomaly maps as a function of satellite altitude, instrument noise level, external noise model, and crustal anomaly field model. A preliminary analysis of the geophysical structure of Broken Ridge is presented and unresolved questions are listed.

  12. Principal facts for gravity stations in Dixie; Fairview, and Stingaree valleys, Churchill and Pershing counties, Nevada

    USGS Publications Warehouse

    Schaefer, D.H.; Thomas, J.M.; Duffrin, B.G.

    1984-01-01

    During March through July 1979, gravity measurements were made at 300 stations in Dixie Valley, Nevada. In December 1981, 45 additional stations were added--7 in Dixie Valley, 23 in Fairview Valley, and 15 in Stingaree Valley. Most altitudes were determined by using altimeters or topographic maps. The gravity observations were made with a Worden temperature-controlled gravimeter with an initial scale factor of 0.0965 milliGal/scale division. Principal facts for each of the 345 stations are tabulated; they consist of latitude, longitude, altitude, observed gravity, free-air anomaly, terrain correction, and Bouguer anomaly values at a bedrock density of 2.67 grams/cu cm. (Lantz-PTT)

  13. Geoid undulations and gravity anomalies over the Aral Sea, the Black Sea and the Caspian Sea from a combined GEOS-3/SEASAT/GEOSAT altimeter data set

    NASA Technical Reports Server (NTRS)

    Au, Andrew Y.; Brown, Richard D.; Welker, Jean E.

    1991-01-01

    Satellite-based altimetric data taken by GOES-3, SEASAT, and GEOSAT over the Aral Sea, the Black Sea, and the Caspian Sea are analyzed and a least squares collocation technique is used to predict the geoid undulations on a 0.25x0.25 deg. grid and to transform these geoid undulations to free air gravity anomalies. Rapp's 180x180 geopotential model is used as the reference surface for the collocation procedure. The result of geoid to gravity transformation is, however, sensitive to the information content of the reference geopotential model used. For example, considerable detailed surface gravity data were incorporated into the reference model over the Black Sea, resulting in a reference model with significant information content at short wavelengths. Thus, estimation of short wavelength gravity anomalies from gridded geoid heights is generally reliable over regions such as the Black Sea, using the conventional collocation technique with local empirical covariance functions. Over regions such as the Caspian Sea, where detailed surface data are generally not incorporated into the reference model, unconventional techniques are needed to obtain reliable gravity anomalies. Based on the predicted gravity anomalies over these inland seas, speculative tectonic structures are identified and geophysical processes are inferred.

  14. Accuracy of the determination of mean anomalies and mean geoid undulations from a satellite gravity field mapping mission

    NASA Technical Reports Server (NTRS)

    Jekeli, C.; Rapp, R. H.

    1980-01-01

    Improved knowledge of the Earth's gravity field was obtained from new and improved satellite measurements such as satellite to satellite tracking and gradiometry. This improvement was examined by estimating the accuracy of the determination of mean anomalies and mean undulations in various size blocks based on an assumed mission. In this report the accuracy is considered through a commission error due to measurement noise propagation and a truncation error due to unobservable higher degree terms in the geopotential. To do this the spectrum of the measurement was related to the spectrum of the disturbing potential of the Earth's gravity field. Equations were derived for a low-low (radial or horizontal separation) mission and a gradiometer mission. For a low-low mission of six month's duration, at an altitude of 160 km, with a data noise of plus or minus 1 micrometers sec for a four second integration time, we would expect to determine 1 deg x 1 deg mean anomalies to an accuracy of plus or minus 2.3 mgals and 1 deg x 1 deg mean geoid undulations to plus or minus 4.3 cm. A very fast Fortran program is available to study various mission configurations and block sizes.

  15. Comparative study of compensation mechanism of lunar impact basins from new gravity field model of SELENE (Kaguya)

    NASA Astrophysics Data System (ADS)

    Namiki, N.; Sugita, S.; Matsumoto, K.; Goossens, S.; Ishihara, Y.; Noda, H.; Ssasaki, S.; Iwata, T.; Hanada, H.; Araki, H.

    2009-04-01

    The gravity field is a fundamental physical quantity for the study of the internal structure and the evolution of planetary bodies. The most significant problem of the previous lunar gravity models, however, is the lack of direct observations of the far side gravity signals [1]. We then developed a satellite-to-satellite Doppler tracking sub-system for SELENE [2]. In this study, we adopt our new gravity field model with nearly full coverage of the lunar far side to discuss dichotomy of the lunar basins. Because all the nearside impact basins are filled with extensive mare basalt deposits, it is difficult to estimate the subsurface structures, such as uplift of the Moho surface, from gravity measurements. In contrast, far-side impact basins have much less or no mare basalt coverage. This may allow us to investigate the internal structure underneath impact basins. Such knowledge will be important in understanding the response of a solid planetary body to large meteoritic impacts and also the thermal state of the Moon during the late heavy bombardment period. There are distinctive differences between the anomalies of the near side principal mascons and the far side basins. As shown previously [1, 3], the near side principal mascons have sharp shoulders with a gravity plateau and a weakly negative gravity anomaly in the surroundings. In contrast, the far side basins are characterized by concentric rings of positive and negative anomalies. The circular gravity highs agree well with the topographic rims of the basins revealed by SELENE topography model STM-359_grid-02 [4]. In our gravity model, Orientale, Mendel-Rydberg, Lorentz, and Humboldtianum show more affinity with the far side basins than the near side principal mascons [5]. Korolev, Mendeleev, Planck, and Lorentz basins have sharp central peaks of which magnitude in free-air anomalies is almost equivalent to the one in Bouguer anomalies. On the other hand, Orientale, Mendel-Rydberg, Humboldtianum, Moscoviense

  16. Gravity measurements and terrain corrections using a digital terrain model in the NW Himalaya

    NASA Astrophysics Data System (ADS)

    Banerjee, Paramesh

    1998-12-01

    Areas recently gravity surveyed in the NW Himalaya are characterized by high-elevation and high-amplitude topographic undulations. A new method of applying combined Bouguer and terrain corrections using a digital terrain model is highly accurate and offers advantages over conventional techniques by saving efforts and being more flexible. Partitioning parameters for station-dependent inner-zone compartments and station-independent outer zones can be optimally selected for the desired accuracy requirements. A digital terrain database is used to obtain the outer-zone corrections. In the situation of the NW Himalaya surveys, a 1.2 km inner zone is divided into 112 compartments for each station and a digital terrain database containing nearly 16 000 data points for 30″×30″ compartments was applied using the computer program EFFECT.FOR, to compute combined Bouguer and terrain corrections for a 20 km range. The terrain corrections between 20 and 170 km were computed using National Geophysical Data Centre (NGDC) 5'×5' gridded global elevation database. The magnitude of the terrain correction varies between 3 and 50 mGal. The effects of the 20 km range terrain correction are more pronounced on short-medium wavelength anomalies. The Swarghat gravity high is further enhanced while several high-frequency pseudo-anomalies disappear after applying the terrain corrections. The refined Bouguer anomaly varies from -160 mGal at the southern end of the section, to -310 mGal at the northern end, suggesting a Moho depth variation from 45 to nearly 60 km. The steepness of the northward negative gravity gradient, typical for the Himalaya, is considerably reduced after applying a terrain correction for the 170 km range.

  17. Analysis of converted S-waves and gravity anomaly along the Aegir Ridge: implications for crustal lithology

    NASA Astrophysics Data System (ADS)

    Rai, A. K.; Breivik, A. J.; Mjelde, R.; Hanan, B. B.; Ito, G.; Sayit, K.; Howell, S.; Vogt, P. R.; Pedersen, R.

    2012-12-01

    The Aegir Ridge is an extinct spreading ridge in North-East Atlantic ocean. A thinner than normal crust around the Aegir Ridge appears as a hole in the extensively magmatic surroundings. Its proximity to the Iceland hot-spot makes it particularly important for understanding the changing dynamics of hotspot-ridge interaction. An integrated seismic and dredging experiment was conduced during the summer of 2010 with the primary aim to understand the nature of magmatism along the ridge shortly before cessation of seafloor spreading through variations of sub-seafloor lithological properties. Here, we present results of analysis of converted shear-waves recorded on OBS-sesimic data, and ship-gravity data. The shear-wave study enables us to quantify the variation of Vp/Vs in the sediments, crust and the upper-most mantle. We also inverted the gravity data to determine the sub-seafloor density distribution. The P- to S- converted shear-waves were identified on 20 OBSs along a profile with a total length of 550 km parallel to the ridge-axis. The sedimentary section on top of the crystalline crust is well illuminated in the streamer data. The forward modelling of the OBS data reveals that the Vp/Vs ratio in sediments are as high as 4.8, decreasing rapidly to a value of 3.00, primarily due to compaction of sediments with depth. Identification of sufficient PnS and PSn phases enable us to model the crustal and upper-most mantle Vp/Vs. The upper crystalline crust requires a Vp/Vs value of 1.99 and 1.89 for the southern and the northern profiles respectively, to fit the observations. The lower crust and upper-most part of the mantle have a Vp/Vs of ~1.82 and 1.795 respectively. Slightly lower Vp and moderate increase in Vp/Vs in parts of the crust and upper mantle presumably indicate presence of faulting, fracturing in the crust and moderate degree of serpentinization of the upper mantle. A sub-seafloor density model is derived by non-linear inversion of the gravity anomaly. The

  18. Dip distribution of Oita-Kumamoto Tectonic Line located in central Kyushu, Japan, estimated by eigenvectors of gravity gradient tensor

    NASA Astrophysics Data System (ADS)

    Kusumoto, Shigekazu

    2016-09-01

    We estimated the dip distribution of Oita-Kumamoto Tectonic Line located in central Kyushu, Japan, by using the dip of the maximum eigenvector of the gravity gradient tensor. A series of earthquakes in Kumamoto and Oita beginning on 14 April 2016 occurred along this tectonic line, the largest of which was M = 7.3. Because a gravity gradiometry survey has not been conducted in the study area, we calculated the gravity gradient tensor from the Bouguer gravity anomaly and employed it to the analysis. The general dip distribution of the Oita-Kumamoto Tectonic Line was found to be about 65° and tends to be higher towards its eastern end. In addition, we estimated the dip around the largest earthquake to be about 60° from the gravity gradient tensor. This result agrees with the dip of the earthquake source fault obtained by Global Navigation Satellite System data analysis.[Figure not available: see fulltext.

  19. Use of gravity potential field methods for defining a shallow magmatic intrusion: the Mt. Amiata case history (Tuscany, Central Italy)

    NASA Astrophysics Data System (ADS)

    Girolami, Chiara; Rinaldo Barchi, Massimiliano; Pauselli, Cristina; Heyde, Ingo

    2016-04-01

    We analyzed the Bouguer gravity anomaly signal beneath the Mt. Amiata area in order to reconstruct the subsurface setting. The study area is characterized by a pronounced gravity minimum, possibly correlated with the observed anomalous heat flow and hydrothermal activity. Using different approaches, previous authors defined a low density body (generally interpreted as a magmatic intrusion) beneath this area, which could explain the observed gravity anomaly minimum. However the proposed geologic models show different geometries and densities for the batholith. The gravity data used in this study (kindly provided by eni) were acquired from different institutions (eni, OGS, USDMA and Servizio Geologico d'Italia) and collected in a unique dataset, consisting of about 50000 stations, randomly distributed, which cover Central Italy, with a spacing of less than 1 km. For each station the elevation and the Bouguer gravity anomaly data are given. From this dataset, we created two maps of the Bouguer gravity anomaly and the topography, using the Minimum Curvature gridding method considering a grid cell size of 500m x 500m. The Bouguer gravity anomaly has been computed using a density of 2.67 g/cm3. From these maps we extracted a window of about 240 km2 (12x20 km) for the study area, which includes the Mt. Amiata region and the adjacent Radicofani sedimentary basin. The first part of this study was focused on calculating the first order vertical derivative and the power spectra analysis of the Bouguer gravity anomaly to enhance the effect of shallow bodies and estimating the source depth respectively. The second part of this study was focused on constructing a 3D geological density model of the subsurface setting of the studied area, implementing a forward modelling approach. The stratigraphy of the study area's upper crust schematically consists of six litho-mechanical units, whose density was derived from velocity data collected by active seismic surveys. A preliminary

  20. Analysis of gravimetric anomalies in Furnas caldera (São Miguel, Azores)

    NASA Astrophysics Data System (ADS)

    Montesinos, F. G.; Camacho, A. G.; Vieira, R.

    1999-09-01

    Furnas Volcano (São Miguel Island, Azores) is a steep-sided caldera complex resulting from several collapses. In this paper, we analyse and interpret the gravity survey carried out by the Instituto de Astronomı´a y Geodesia (Spain) and the gravity data published by the Instituto Nacional de Meteorologia e Geofisica (Portugal). The resulting Bouguer anomaly reveals the presence of a regional trend, several local features and a component of noise. In separating the regional trend we use a robust polynomial fitting. Further, a covariance analysis and a least squares prediction are applied to filter the noise and to model the local anomaly. A first signal map represents the main local anomaly, while the secondary signal map shows superficial anomalies. This distribution reveals a local main minimum close to the 1630 A.D. and Gaspar craters. Several possible alignments are shown that lead to a model, mainly with SW-NE and SE-NW orientations, of the negative anomaly, with the pattern of the low density zones showing a relationship with the volcanic features. Applying a stabilized linear method of gravimetric inversion, we obtain a density contrast distribution of the sources of the filtered local Bouguer anomaly, considering as unknowns the anomalous densities of a fixed discrete distribution of rectangular prisms which represents the subsoil volume. A mixed minimization criteria for the weighted residuals and the weighted density contrast allow us to obtain a solution as a discrete three-dimensional density contrast model. The obtained anomalous densities model shows a clear relation with the structure of the caldera complex and tectonic trends, with the principal body of negative contrast density being associated with the subsurface structure of the caldera.

  1. Detailed gravity and aeromagnetic surveys in the Black Rock Desert Area, Utah. Topical report

    SciTech Connect

    Serpa, L.F.; Cook, K.L.

    1980-01-01

    Aeromagnetic and gravity surveys were conducted during 1978 in the Black Rock Desert, Utah over an area of about 2400 km/sup 2/ between the north-trending Pavant and Cricket Mountains. The surveys assisted in evaluating the geothermal resources in the Meadow-Hatton Known Geothermal Resource Area (KGRA) and vicinity by delineating geophysical characteristics of the subsurface. The gravity measurements from approximately 700 new stations were reduced to complete Bouguer gravity anomaly values with the aid of a computerized terrain-correction program and contoured at an interval of 1 milligal. The aeromagnetic survey was drape flown at an altitude of 305 m (1000 ft) and a total intensity residual aeromagnetic map with a contour interval of 20 gammas was produced. Two gravity and aeromagnetic east-west profiles and one north-south profile were modeled using a simultaneous 2 1/2-dimensional modeling technique to provide a single model satisfying both types of geophysical data.

  2. Application of high-pass filtering techniques on gravity and magnetic data of the eastern Qattara Depression area, Western Desert, Egypt

    NASA Astrophysics Data System (ADS)

    Zahra, Hesham Shaker; Oweis, Hesham T.

    2016-06-01

    In this work, a reconnaissance study is presented to delineate the subsurface tectonics and lithological inferences of the eastern area of Qattara Depression using the Bouguer gravity and aeromagnetic data. To achieve this goal, several transformation techniques and filtering processes are accomplished on these maps. At first, the total intensity aeromagnetic map is processed through the application of reduction to the magnetic north pole technique. The fast Fourier transform is carried out on the gravity and RTP magnetic data for establishing and defining the residual (shallow) sources. The frequency high-pass filtering is used to enhance the anomaly wavelengths associated with the shallow sources. The used processing techniques are the polynomial surface fitting enhancement, Laplacian, Strike Filtering, Enhancement Utilization, Suppression Utilization, Butterworth Filtering Utilization, Butterworth high-pass filter, Euler's deconvolution and forward modeling. The equivalent depths of the isolated short wavelength anomalies are 0.759 and 0.340 km below the flight surface, and the depths of the intermediate wavelength anomalies are 1.28 and 2.00 km for the gravity and magnetic data, respectively. Finally, the quantitative interpretations of the Bouguer gravity and RTP magnetic maps of the study area, reflect the occurrence of the various types of structures and their components. The main tectonic deformations of the study area have NNW-SSE, NNE-SSW, NE-SW, NW-SE and E-W trends.

  3. Gravity gradient for Greenland and its tectonic interpretation

    NASA Astrophysics Data System (ADS)

    Grushinsky, Andrew N.

    2013-04-01

    Gravity gradient is the indicator of the stress conditions in the lithosphere. The axis of gradient signs changing indicates the boundary of blocks exposed to different tensions. The lines of maxima and minima of gravity gradient correspondingly marked the boundary of zones of compression and expansion. Four various types of the gravity anomalies was calculated: in free air, Bouguer's, Glennie's and isostatic. And then was calculated their gradients. The preliminary analysis of gradients shows, that its qualitative behavior for all types of gravity anomalies is very closely and, therefore, conclusions about the stress conditions in the lithosphere of the considering region are definite. Range of the changing for gradients of gravity in free air anomalies - from -96.1 to 135.8 eötvös, and for gradients of gravity Bouguer's anomalies - from -122.6 to 141.9 eötvös. Range of the changing for gradients of gravity Glennie's and isostatic anomalies are substantially smaller, for gradients of gravity Glennie's anomalies - from -27.6 to 25.5 eötvös, and for gradients of gravity isostatic anomalies - from -19.2 to 21.2 eötvös. This difference in the gradient values, evidently, connects with the difference in the thoroughness and the degree of averaging of the anomalies. Analysis of gravity gradient shown the following: 1. In the western part of the researching region are distinguished three linear structures (two maxima and one minimum), which marked rift zone of the Baffin Bay and Davis Strait. This disappeared rift characterized by depressed zone, lengthened from Nares strait along the west sea coast of Greenland. In the south part of this zone localized deep fault, which northward become lesser expressed. To the north and north-east from the Nares strait lengthened to the North Pole zone of compression, blocked up existing previously rift, by which the rotation of the Greenland part of Canadian shield from its cardinal part happened. Center of this rotation

  4. Structure of the midcontinent basement. Topography, gravity, seismic, and remote sensing

    NASA Technical Reports Server (NTRS)

    Guinness, E. A.; Strebeck, J. W.; Arvidson, R. E.; Scholz, K.; Davies, G. F.

    1981-01-01

    Some 600,000 discrete Bouguer gravity estimates of the continental United States were spatially filtered to produce a continuous tone image. The filtered data were also digitally painted in color coded form onto a shaded relief map. The resultant image is a colored shaded relief map where the hue and saturation of a given image element is controlled by the value of the Bouguer anomaly. Major structural features (e.g., midcontinent gravity high) are readily discernible in these data, as are a number of subtle and previously unrecognized features. A linear gravity low that is approximately 120 to 150 km wide extends from southeastern Nebraska, at a break in the midcontinent gravity high, through the Ozark Plateau, and across the Mississippi embayment. The low is also aligned with the Lewis and Clark lineament (Montana to Washington), forming a linear feature of approximately 2800 km in length. In southeastern Missouri the gravity low has an amplitude of 30 milligals, a value that is too high to be explained by simple valley fill by sedimentary rocks.

  5. Tectonic history of the north portion of the San Andreas fault system, California, inferred from gravity and magnetic anomalies

    USGS Publications Warehouse

    Griscom, A.; Jachens, R.C.

    1989-01-01

    Geologic and geophysical data for the San Andreas fault system north of San Francisco suggest that the eastern boundary of the Pacific plate migrated eastward from its presumed original position at the base of the continental slope to its present position along the San Andreas transform fault by means of a series of eastward jumps of the Mendocino triple junction. These eastward jumps total a distance of about 150 km since 29 Ma. Correlation of right-laterally displaced gravity and magnetic anomalies that now have components at San Francisco and on the shelf north of Point Arena indicates that the presently active strand of the San Andreas fault north of the San Francisco peninsula formed recently at about 5 Ma when the triple junction jumped eastward a minimum of 100 km to its present location at the north end of the San Andreas fault. -from Authors

  6. Spherical-earth gravity and magnetic anomaly modeling by Gauss-Legendre quadrature integration

    NASA Technical Reports Server (NTRS)

    Von Frese, R. R. B.; Hinze, W. J.; Braile, L. W.; Luca, A. J.

    1981-01-01

    Gauss-Legendre quadrature integration is used to calculate the anomalous potential of gravity and magnetic fields and their spatial derivatives on a spherical earth. The procedure involves representation of the anomalous source as a distribution of equivalent point gravity poles or point magnetic dipoles. The distribution of equivalent point sources is determined directly from the volume limits of the anomalous body. The variable limits of integration for an arbitrarily shaped body are obtained from interpolations performed on a set of body points which approximate the body's surface envelope. The versatility of the method is shown by its ability to treat physical property variations within the source volume as well as variable magnetic fields over the source and observation surface. Examples are provided which illustrate the capabilities of the technique, including a preliminary modeling of potential field signatures for the Mississippi embayment crustal structure at 450 km.

  7. Spherical-earth Gravity and Magnetic Anomaly Modeling by Gauss-legendre Quadrature Integration

    NASA Technical Reports Server (NTRS)

    Vonfrese, R. R. B.; Hinze, W. J.; Braile, L. W.; Luca, A. J. (Principal Investigator)

    1981-01-01

    The anomalous potential of gravity and magnetic fields and their spatial derivatives on a spherical Earth for an arbitrary body represented by an equivalent point source distribution of gravity poles or magnetic dipoles were calculated. The distribution of equivalent point sources was determined directly from the coordinate limits of the source volume. Variable integration limits for an arbitrarily shaped body are derived from interpolation of points which approximate the body's surface envelope. The versatility of the method is enhanced by the ability to treat physical property variations within the source volume and to consider variable magnetic fields over the source and observation surface. A number of examples verify and illustrate the capabilities of the technique, including preliminary modeling of potential field signatures for Mississippi embayment crustal structure at satellite elevations.

  8. Gorringe Ridge gravity and magnetic anomalies are compatible with thrusting at a crustal scale

    NASA Astrophysics Data System (ADS)

    Galindo-Zaldívar, J.; Maldonado, A.; Schreider, A. A.

    2003-06-01

    The main features of the deep structure of the Gorringe Ridge are analysed on the basis of gravity and magnetic measurements, as well as seismic profiles, drill holes, rock dredges, submersible observations and seismicity data. The gravity and magnetic models of the Gettysburg and Ormonde seamounts, which form the Gorringe Ridge, suggest that the Moho is approximately flat and the upper part of the ridge corresponds to a northwestwards vergent fold. This structure is the result of a northwestward vergent thrust that deformed the oceanic crust, with a minimum slip of approximately 20 km. The activity of the thrust probably started 20 Myr, and produced the recent stages of seamount uplift. The seamount is mainly composed of gabbros of the oceanic crust, serpentinized rocks and alkaline basalts. The large antiform, located in the hangingwall of the thrust, is probably deformed by minor faults. This oceanic ridge is a consequence of the oblique convergence between the African Plate and the overlapping Eurasian Plate.

  9. Three-dimensional density interface inversion of gravity anomalies in the spectral domain

    NASA Astrophysics Data System (ADS)

    Feng, Juan; Meng, Xiaohong; Chen, Zhaoxi; Zhang, Sheng

    2014-06-01

    Based on the Fourier transform, the Parker-Oldenburg algorithm in the frequency domain was extended for the three-dimensional case where the density changes with depth. From this, a gravity interface inversion formula was derived in which the assumed density can be varied laterally and vertically. Iterative convergence is assured by fixing a particular depth as the datum plane below the surface to reduce the interface fluctuation. The results of an example set of synthetic gravity data indicate that the proposed method gives high precision and rapid convergence, with high practical value for the inversion of density interfaces. This method was also used to determine the Moho depth beneath northern China. The results were confirmed by seismic sounding data. Differences between seismic sounding data and inverted depth were insignificant and were in the range of -0.92-1.67 km.

  10. Improved global prediction of 300 nautical mile mean free air anomalies

    NASA Technical Reports Server (NTRS)

    Cruz, J. Y.

    1982-01-01

    Current procedures used for the global prediction of 300nm mean anomalies starting from known values of 1 deg by 1 deg mean anomalies yield unreasonable prediction results when applied to 300nm blocks which have a rapidly varying gravity anomaly field and which contain relatively few observed 60nm blocks. Improvement of overall 300nm anomaly prediction is first achieved by using area-weighted as opposed to unweighted averaging of the 25 generated 60nm mean anomalies inside the 300nm block. Then, improvement of prediction over rough 300nm blocks is realized through the use of fully known 1 deg by 1 deg mean elevations, taking advantage of the correlation that locally exists between 60nm mean anomalies and 60nm mean elevations inside the 300nm block. An improved prediction model which adapts itself to the roughness of the local anomaly field is found to be the model of Least Squares Collocation with systematic parameters, the systematic parameter being the slope b which is a type of Bouguer slope expressing the correlation that locally exists between 60nm mean anomalies and 60nm mean elevations.

  11. Lithology identification with gravity and magnetic anomalies for mine exploration in the China-Mongolia border

    NASA Astrophysics Data System (ADS)

    Meng, X.; Wang, J.

    2015-12-01

    China-Mongolia border is an important metallogenic province, its structural is complex and the study of it is of great significance for future detecting. In the last three years, we have conducted gravity and magnetic survey in the eastern segment of the China-Mongolia border along the profile, hoping to get a detailed characterization of the subsurface of this area. In this study, we conducted lithology identification in this area with measured gravity and magnetic data. In our work, topological calculations were performed on inversion data and physical property data for lithology identification. Our work can be summarized into the following steps: Firstly, the rock density and magnetic susceptibility near the survey profiles were summarized by field reconnaissance, and the lithology was divided into several types. Thus, a correspondence between lithology and physical properties was defined to some extent. Secondly, different mapping equations were established according to the physical properties for each lithology.Then, inversion of the gravity and magnetic data have been performed to get the physical properties (density and susceptibility) below the profile. Lastly, the lithology was identified through gravity and magnetic inversion result and the mapping equations mentioned above. In our study, the magmatic rocks within 50 km of the lower half space can be divided into four major types based on the identification result. The lithology varies significantly from north to south below this profile. Moreover, the lithology distribution trend and the formation age of the lower half space is summarized based on characteristics of the gravity and magnetic fields and the tectonic setting. For lithology identification with different types of data, we think that identify lithology information by one of the data can be conducted firstly, such as magnetic susceptibility, and then bring the results to lithology identification among the inversion of other data , which greatly

  12. On Different Techniques for the Calculation of Bougher Gravity Anomalies for Joint Inversion of Geophysical Data in the Rio Grande Rift

    NASA Astrophysics Data System (ADS)

    Zamora, A.; Hussein, M. J.; Velasco, A. A.

    2012-12-01

    Density variations in the Earth result from different material properties, which reflect the tectonic processess attributed to a region. Density variations can be identified through measurable material properties, such as seismic velocities, gravity field, magnetic field, etc. Gravity anomaly inversions are particularly sensitive to density variations but suffer from significant non-uniqueness. However, using inverse models with gravity Bougher anomalies and other geophysical data, we can determine three dimensional structural and geological properties of the given area. We explore different techniques for the calculation of Bougher gravity anomalies for their use in joint inversion of multiple geophysical data sets. Various 2- and 3-Dimensional (3-D) gravity profile forward modeling programs have been developed as variations of existing algorithms; these variations have similarities, differences, and strengths and weaknesses. The purpose of this study is to determine the most effective gravity forward modeling method that can be used to combine the information provided by complementary datasets, such as gravity and seismic information, to improve the accuracy and resolution of Earth models obtained for the underlying structure of the Rio Grande Rift. In an effort to determine the most appropriate method to use in a joint inversion algorithm and a data fusion approach currently in development, we test each approach by using a model of the Rio Grande Rift obtained from seismic surface wave dispersion and receiver functions. We find that there are different uncertainties associated with each methodology that affect the accuracy achieved by including gravity profile forward modeling. Moreover, there exists a bigger margin of error associated to the 2-D methods due to the simplification of calculations that do not take into account the 3-D characteristics of the Earth's structure.

  13. Geophysical investigations on the gravity and aeromagnetic anomalies of the region between Sapanca and Duzce, along the North Anatolian Fault, Turkey

    NASA Astrophysics Data System (ADS)

    Tigli, Cigdem Sendur; Ates, Abdullah; Aydemir, Attila

    2012-12-01

    In this paper, it is aimed to model subsurface structures to the east of the Gulf of Izmit through Duzce by using the gravity and aeromagnetic anomaly data. 1/500.000 scaled gravity anomaly map of the area was taken from the General Directorate of Mineral Research and Exploration (MTA) and it was digitized. The aeromagnetic anomaly data were obtained in the digital form. 3D and 2D models were constructed to reveal the subsurface structure in two different inset regions in the study area including most important negative and positive gravity anomalies. Seismic velocities obtained from the deep seismic recordings were converted to densities. In addition, density information from a previous research was also taken. These densities were used for construction of 3D and 2D gravity models where it was shown that there are narrow and long sedimentary basins and depressions with 0.5-3 km depths. These sedimentary basins with the shape of negative flower structures indicating pull-apart basins are controlled by the active fault segments of the North Anatolian Fault (NAF). Earthquake epicenter data were also correlated with the constructed models from the gravity anomalies. Positive gravity anomalies are also caused by very shallow (about 2 km) masses that are accepted as the crustal origin intrusions into the fractures of the NAF and, ophiolites and gabbro outcropping on the surface of the studied regions. These intrusives and remnants of the Tethys Ocean are located between the fault segments where the fault bifurcates and they also constitute barriers for straight extension of the NAF. Analytic signal method was applied to the aeromagnetic anomaly data to determine the locations and boundaries of the causative bodies. Those bodies are observed around Duzce, and to the E-SE of it, to the NW of Golyaka and a large mass between Adapazari and Sapanca. Shallow settlement of these magmatics was confirmed by the second vertical derivative of the aeromagnetic data. An anti

  14. Calculation of Moho Depth by Gravity Anomalies in Qinghai-Tibet Plateau Based on an Improved Iteration of Parker-Oldenburg Inversion

    NASA Astrophysics Data System (ADS)

    Zhang, Chong; Huang, Danian; Wu, Guochao; Ma, Guoqing; Yuan, Yuan; Yu, Ping

    2015-10-01

    A derivative formula for interface inversion using gravity anomalies, combining the Parker-Oldenburg method for calculating and inverting gravity anomalies with Xu's iteration method for continuing potential fields, leads to a convergent inversion algorithm and an optimally located density interface geometry. In this algorithm, no filtering or any other convergence control techniques are needed during iteration. The method readily iterates the variable depth of the gravity interface by means of upward continuation in a form equivalent to inversion iteration in the Fourier domain instead of the divergent, downward continuation term. This iteration algorithm not only efficiently solves the divergence problem in the inversion iteration procedure but also validly obtains an excellent result for the density interface. A numerical example is presented to illustrate perfect execution of this approach in gravity exploration, and a real geophysical example of inversion of the Moho depth by means of this approach using a set of measured gravity anomalies over the Qinghai-Tibet Plateau in China is offered.

  15. New gravity and magnetics map of eastern part of Azores

    NASA Astrophysics Data System (ADS)

    Dehghani, A.

    2013-12-01

    The Azores are of volcanic origin and the volcanic activities are still occurs in the area. The main tectonic features in the eastern part of Azores are the Gloria Fault (GF) and São Miguel volcanic Island. The GF is an E-W strike-slip fault and can be traced by bathymetry. In the past decade many geological and geophysical investigations were dedicated to the study of tectonic features in the eastern part of Azores. Two of these cruises were organized by the Institute of Geophysics, University of Hamburg, Germany, in the years 2009 and 2012. In 2009 during the Meteor cruise M79-2 a total of 5500 km new Gravity and 2000 km new magnetic data were collected along some 60 Profiles. During the Poseidon cruise in the year 2012 some 2000 km new gravity and magnetic data were collected along two E-W profiles in the eastern part of Azores. The new gravity data were recorded with the modern Air-Sea-Gravimeter of Bodenseewerk KSS 31M and the new magnetic date with the Gradiometer SeaSpy. All new potential date were combined with the available data of the data base GEODAS and the new gravity anomaly maps (Free-Air and Bouguer) and the new magnetic anomaly map were produced. The maps show clearly the tectonic features in the area. The GF can be traced very well on both gravity and magnetic anomaly maps. Most of the small hills around the São Miguel Island are shown up in the magnetic anomaly map as strong magnetic anomaly. The new gravity and magnetic maps and the interpretation of them will be presented. The results of some 2-D modeling along some interesting profiles will be also presented and discussed.

  16. New gravity and magnetics map of eastern part of Azores

    NASA Astrophysics Data System (ADS)

    Dehghani, Ali

    2014-05-01

    The Azores are of volcanic origin and the volcanic activities are still occurs in the area. The main tectonic features in the eastern part of Azores are the Gloria Fault (GF) and São Miguel volcanic Island. The GF is an E-W strike-slip fault and can be traced by bathymetry. In the past decade many geological and geophysical investigations were dedicated to the study of tectonic features in the eastern part of Azores. Two of these cruises were organized by the Institute of Geophysics, University of Hamburg, Germany, in the years 2009 and 2012. In 2009 during the Meteor cruise M79-2 a total of 5500 km new Gravity and 2000 km new magnetic data were collected along some 60 Profiles. During the Poseidon cruise in the year 2012 some 2000 km new gravity and magnetic data were collected along two E-W profiles in the eastern part of Azores. The new gravity data were recorded with the modern Air-Sea-Gravimeter of Bodenseewerk KSS 31M and the new magnetic date with the Gradiometer SeaSpy. All new potential date were combined with the available data of the data base GEODAS and the new gravity anomaly maps (Free-Air and Bouguer) and the new magnetic anomaly map were produced. The maps show clearly the tectonic features in the area. The GF can be traced very well on both gravity and magnetic anomaly maps. Most of the small hills around the São Miguel Island are shown up in the magnetic anomaly map as strong magnetic anomaly. The new gravity and magnetic maps and the interpretation of them will be presented. The results of some 2-D modeling along some interesting profiles will be also presented and discussed.

  17. Downward continuation of the free-air gravity anomalies to the ellipsoid using the gradient solution and terrain correction: An attempt of global numerical computations

    NASA Technical Reports Server (NTRS)

    Wang, Y. M.

    1989-01-01

    The formulas for the determination of the coefficients of the spherical harmonic expansion of the disturbing potential of the earth are defined for data given on a sphere. In order to determine the spherical harmonic coefficients, the gravity anomalies have to be analytically downward continued from the earth's surface to a sphere-at least to the ellipsoid. The goal is to continue the gravity anomalies from the earth's surface downward to the ellipsoid using recent elevation models. The basic method for the downward continuation is the gradient solution (the g sub 1 term). The terrain correction was also computed because of the role it can play as a correction term when calculating harmonic coefficients from surface gravity data. The fast Fourier transformation was applied to the computations.

  18. Preliminary gravity investigations of the Wahmonie Site, Nevada Test Site, Nye County, Nevada

    SciTech Connect

    Ponce, D.A.

    1981-12-31

    A gravity survey of the southwest corner of the Nevada Test Site was completed during 1979 to 1980 as part of an effort to characterize a possible radioactive waste storage site in granitic rocks. The survey outlined a large, broad, and flat gravity high centered near Wahmonie Site. Combined geophysical data indicate that the anomalous area is underlain by a dense, magnetic, and possibly intrusive body. Gravity data show a +15 milligal Bouguer anomaly coincident with a large positive aeromagnetic anomaly. The data reveal a prominent fault at the west edge of the inferred intrusive. Both gravity and magnetic anomalous highs extend NNE over a horst composed predominantly of rhyodacite of the Tertiary Salyer Formation. Local aeromagnetic highs are closely associated with two granodiorite exposures on the eastern edge of the horst. A local gravity high of about +2 milligal is centered directly over the southern granodiorite exposure and another high is centered over the northern exposure. A steep gravity gradient outlining the gravity high coincides with the outer edge of a zone of hydrothermal alteration which surrounds the horst. The gravity gradient probably marks the approximate limit of an intrusive body.

  19. Structure of the southern Rio Grande rift from gravity interpretation

    NASA Astrophysics Data System (ADS)

    Daggett, P. H.; Keller, G. R.; Wen, C.-L.; Morgan, P.

    1986-05-01

    Regional Bouguer gravity anomalies in southern New Mexico have been analyzed by two-dimensional wave number filtering and poly-nomial trend surface analysis of the observed gravity field. A prominent, regional oval-shaped positive gravity anomaly was found to be associated with the southern Rio Grande rift. Computer modeling of three regional gravity profiles suggests that this anomaly is due to crustal thinning beneath the southern Rio Grande rift. These models indicate a 25 to 26-km minimum crustal thickness within the rift and suggest that the rift is underlain by a broad zone of anomalously low-density upper mantle. The southern terminus of the anomalous zone is approximately 50 km southwest of El Paso, Texas. A thinning of the rifted crust of 2-3 km relative to the adjacent Basin and Range province indicates an extension of about 9 percent during the formation of the modern southern Rio Grande rift. This extension estimate is consistent with estimates from other data sources. The crustal thinning and anomalous mantle is thought to result from magmatic activity related to surface volcanism and high heat flow in this area.

  20. Calculation of gravity and magnetic anomalies of finite-length right polygonal prisms.

    USGS Publications Warehouse

    Cady, J.W.

    1980-01-01

    An equation is derived for the vertical gravity field due to a homogeneous body with polygonal cross‐section and finite strike‐length. The equation can be separated into the two‐dimensional (2-D) terms of Talwani et al. (1959) and exact terms for the contributions of the ends of the prism. Equations for the magnetic field due to a similar body were derived by Shuey and Pasquale (1973), who coined the term “two‐and‐a‐half dimensional” (2 1/2-D) to describe the geometry. Magnetic intensities are expressed as a vector sum, from which the common dot product formulation can be obtained by binomial expansion.

  1. A new automatic method for estimation of magnetization and density contrast by using three-dimensional (3D) magnetic and gravity anomalies

    NASA Astrophysics Data System (ADS)

    Bektas, Ozcan; Ates, Abdullah; Aydemir, Attila

    2012-09-01

    In this paper, a new method estimating the ratio of magnetic intensity to density contrast of a body that creates magnetic and gravity anomalies is presented. Although magnetic intensity and density of an anomalous body can be measured in the laboratory from the surface samples, the proposed new method is developed to determine the magnetic intensity and density contrast from the magnetic and gravity anomalies when the surface samples are not available. In this method, density contrast diagrams of a synthetic model are produced and these diagrams are prepared as graphics where the magnetic intensity (J) is given in the vertical axis and Psg (pseudogravity)/Grv (gravity) values in horizontal axis. The density contrast diagrams can be prepared as three sub-diagrams to show the low, middle and high ranges allowing obtain density contrast of body. The proposed method is successfully tested on the synthetic models with and without error. In order to verify the results of the method, an alternative method known as root-mean-square (RMS) is also applied onto the same models to determine the density contrast. In this manner, maximum correlation between the observed gravity and calculated gravity anomalies is searched and confirmation of the results is supported with the RMS method. In order to check the reliability of the new method on the field data, the proposed method is applied to the Tetbury (England) and Hanobasi (Central Turkey) magnetic and gravity anomalies. Field models are correlated with available geological, seismic and borehole data. The results are found consistent and reliable for estimating the magnetic intensity and density contrast of the causative bodies.

  2. Preliminary isostatic residual gravity anomaly map of Paso Robles 30 x 60 minute quadrangle, California

    USGS Publications Warehouse

    McPhee, D.K.; Langenheim, V.E.; Watt, J.T.

    2011-01-01

    This isostatic residual gravity map is part of an effort to map the three-dimensional distribution of rocks in the central California Coast Ranges and will serve as a basis for modeling the shape of basins and for determining the location and geometry of faults within the Paso Robles quadrangle. Local spatial variations in the Earth\\'s gravity field, after accounting for variations caused by elevation, terrain, and deep crustal structure reflect the distribution of densities in the mid- to upper crust. Densities often can be related to rock type, and abrupt spatial changes in density commonly mark lithological or structural boundaries. High-density rocks exposed within the central Coast Ranges include Mesozoic granitic rocks (exposed northwest of Paso Robles), Jurassic to Cretaceous marine strata of the Great Valley Sequence (exposed primarily northeast of the San Andreas fault), and Mesozoic sedimentary and volcanic rocks of the Franciscan Complex [exposed in the Santa Lucia Range and northeast of the San Andreas fault (SAF) near Parkfield, California]. Alluvial sediments and Tertiary sedimentary rocks are characterized by low densities; however, with increasing depth of burial and age, the densities of these rocks may become indistinguishable from those of older basement rocks.

  3. Gravity field of Kuwait and its relevance to major geological structures

    SciTech Connect

    Warsi, W.E.K. )

    1990-10-01

    Regional gravity surveys were done in the state of Kuwait during 1986-1988. The new gravity maps show a good correlation with geomorphological features as well as with deeper geological structures. The free-air anomaly map clearly reflects the topography of the Jal Az Zor and Ahmadi ridges, and Wadi Al-Batin. The Bouguer anomaly map is dominated by two prominent gravity highs correlatable with subsurface structural arches. The north-trending gravity high in eastern Kuwait represents the effect of a major structure, the Kuwait arch, along which many important oil fields are located. A smaller northwest-trending high mapped in western Kuwait indicates the presence of a second subsurface arch, which in this paper is named the Dibdibba arch. The two gravity highs are separated by a wedge-shaped gravity low presumably caused by thicker sediments of the Dibdibba basin. Magnetic measurements along selected profiles show the two arches to be associated with 100-200-nT (nannotesla) anomalies apparently reflecting the positive subsurface relief of the crystalline basement. Along the length of the Kuwait arch, magnetic data also indicate lateral susceptibility variations possibly related to lithological variations within the basement.

  4. On the gravitational potential and field anomalies due to thin mass layers

    NASA Technical Reports Server (NTRS)

    Ockendon, J. R.; Turcotte, D. L.

    1977-01-01

    The gravitational potential and field anomalies for thin mass layers are derived using the technique of matched asymptotic expansions. An inner solution is obtained using an expansion in powers of the thickness and it is shown that the outer solution is given by a surface distribution of mass sources and dipoles. Coefficients are evaluated by matching the inner expansion of the outer solution with the outer expansion of the inner solution. The leading term in the inner expansion for the normal gravitational field gives the Bouguer formula. The leading term in the expansion for the gravitational potential gives an expression for the perturbation to the geoid. The predictions given by this term are compared with measurements by satellite altimetry. The second-order terms in the expansion for the gravitational field are required to predict the gravity anomaly at a continental margin. The results are compared with observations.

  5. Isostasy, Stress and Gravitational Potential Energy in the Southern Atlantic - Insights from Satellite Gravity Observations

    NASA Astrophysics Data System (ADS)

    Goetze, H. J.; Klinge, L.; Scheck-Wenderoth, M.; Dressel, I.; Sippel, J.

    2015-12-01

    New satellite gravity fields e.g. EGM2008, GoCo3S and very recently EIGEN-6C4 (Förste et al., 2014) provide high-accuracy and globally uniform information of the Earth's gravity field and partly of its gradients. The main goal of this study is to investigate the impact of this new gravity field and its processed anomalies (Bouguer, Free-air and Vening-Meinesz residual fields) on lithospheric modelling of passive plate margins in the area of the Southern Atlantic. In an area fixed by the latitudes 20° N - 50° S and longitudes 70° W - 20° E we calculated station-complete Bouguer anomalies (bathymetry/topography corrected) both on- and offshore and compared them with the gravity effect of a velocity model which bases on S - waves tomography (Schaeffer and Lebedev, 2013). The corresponding maps provide more insight in the abnormal mass distribution of oceanic lithosphere and the ocean-continent transition zones on both sides of the Atlantic Ocean than Free-air anomalies which are masked by bathymetry. In a next step we calculated isostatic residual fields (Vening-Meinesz isostasy with regard to different lithospheric rigidities) to remove global components (long wavelengths) from the satellite gravity. The Isostatic residual field will be compared with the GPE (gravitational potential energy). GPE variations in the Southern Atlantic, relative to the reference state, were calculated as ΔGPE. Often the oceanic lithosphere is characterized by negative ∆GPE values indicating that the ocean basin is in compression. Differences from this observation will be compared with the state of stress in the area of the passive margins of South America and South Africa and the oceanic lithosphere in between. Schaeffer, A. J. and S. Lebedev, Global shear-speed structure of the upper mantle and transition zone. Geophys. J. Int., 194 (1), 417-449, 2013. doi:10.1093/gji/ggt095

  6. Geologic structure of the northern New Caledonia ridge, as inferred from magnetic and gravity anomalies

    USGS Publications Warehouse

    Collot, J.-Y.; Rigolot, P.; Missegue, F.

    1988-01-01

    Bathymetric, gravity, and magnetic data collected in the southwest Pacific Ocean over the northern New Caledonia ridge show that the main geological units known from the island of New Caledonia extend northward from this island, beneath the Grand Lagon Nord, the Grand Passage, and the d'Entrecasteaux reefs. These data support the model of tectonic evolution of the New Caledonia region proposed by Kroenke (1984). Differences in structure, geophysical signatures and morphology evident between areas north and those south of the Grand Passage, together with the nearness of the Le Noroit massif west of the Grand Passage, suggest that contemporaneously with Eocene to early Oligocene subduction along the western New Caledonia margin, an arc-ridge collision may have occurred near the northern termination of this subduction zone. -from Authors

  7. The alpine Swiss-French airborne gravity survey

    NASA Astrophysics Data System (ADS)

    Verdun, Jérôme; Klingelé, Emile E.; Bayer, Roger; Cocard, Marc; Geiger, Alain; Kahle, Hans-Gert

    2003-01-01

    In February 1998, a regional-scale, airborne gravity survey was carried out over the French Occidental Alps within the framework of the GéoFrance 3-D research program.The survey consisted of 18 NS and 16 EW oriented lines with a spacing of 10 and 20 km respectively, covering the whole of the Western French Alps (total area: 50 000 km2; total distance of lines flown: 10 000 km). The equipment was mounted in a medium-size aircraft (DeHavilland Twin Otter) flowing at a constant altitude of 5100 m a.s.l, and at a mean ground speed of about 280 km h-1. Gravity was measured using a LaCoste & Romberg relative, air/sea gravimeter (type SA) mounted on a laser gyro stabilized platform. Data from 5 GPS antennae located on fuselage and wings and 7 ground-based GPS reference stations were used to determine position and aircraft induced accelerations.The gravimeter passband was derived by comparing the vertical accelerations provided by the gravimeter with those estimated from the GPS positions. This comparison showed that the gravimeter is not sensitive to very short wavelength aircraft accelerations, and therefore a simplified formulation for computing airborne gravity measurements was developed. The intermediate and short wavelength, non-gravitational accelerations were eliminated by means of digital, exponential low-pass filters (cut-off wavelength: 16 km). An important issue in airborne gravimetry is the reliability of the airborne gravity surveys when compared to ground surveys. In our studied area, the differences between the airborne-acquired Bouguer anomaly and the ground upward-continued Bouguer anomaly of the Alps shows a good agreement: the rms of these differences is equal to 7.68 mGal for a spatial resolution of 8 km. However, in some areas with rugged topography, the amplitudes of those differences have a striking correlation with the topography. We then argue that the choice of an appropriate density (reduction by a factor of 10 per cent) for computing the

  8. New gravity maps of the Eastern Alps and significance for the crustal structures

    NASA Astrophysics Data System (ADS)

    Zanolla, Claudio; Braitenberg, Carla; Ebbing, Jörg; Bernabini, Marcello; Bram, Kurt; Gabriel, Gerald; Götze, Hans-Jürgen; Giammetti, Salvatore; Meurers, Bruno; Nicolich, Rinaldo; Palmieri, Franco

    2006-02-01

    The deep seismic profile T RANSALP crosses, from north to south, Germany, Austria and Italy. The gravity measurements for each country were made by national agencies with different reference systems and data reduction methods. Within the frame of the T RANSALP-project a comprehensive database of the Eastern Alps was compiled covering an area of 3.5° by 4° in longitude and latitude (275 by 445 km), respectively. To increase the data coverage in the south Alpine area two gravity surveys were carried out, resulting in 469 areally distributed new stations, of which 215 have been measured with the intent to improve the geoid in the area of the planned Brenner Basistunnel (BBT). The resulting gravity database is the best in terms of resolution and data quality presently available for the Eastern Alps. Here the free air, Bouguer and isostatic gravity fields are critically discussed. The spatial density of existing gravity stations in the three countries is discussed. On the Italian side of the Alps the spatial density is rather sparse compared to the Austrian side. The Bouguer-gravity field varies between - 190 * 10 - 5 m/s 2 and + 25 * 10 - 5 m/s 2, with the minimum located along the Alpine high topographic chain, but with a small offset (a few tens of km) to the greatest topographic elevation, showing that the Airy-type local isostatic equilibrium does not fully apply here. The maximum of the Bouguer anomaly has an elongated shape of 100 by 50 km located between the towns of Verona and Vicenza and covers the Venetian Tertiary Volcanic Province (VTVP), a feature not directly related to the plate collision in the Eastern Alps. The gravity high is only partly explainable by high-density magmatic rocks and requires also a deeper source, like a shallowing of the Moho. The isostatic residual anomalies (Airy model) are in the range ± 50 * 10 - 5 m/s 2, with the greatest positive anomaly corresponding to the location of the VTVP, indicating here under-compensation of masses

  9. Regional lunar gravity anomaly recovery with the GRAIL Level-1b data, and pin-point crustal density estimation with the GRAIL Level-2 and LRO topography data

    NASA Astrophysics Data System (ADS)

    Hashimoto, M.; Heki, K.

    2014-12-01

    We report the lunar gravity anomaly recovery using the GRAIL Level-1b and Level-2 data, downloaded from the PDS Geoscience Node at the Washington University. First, we used the GNV1b (satellite position data) and KBR1b (inter-satellite ranging data) files of the Level-1b data to estimate the surface mass distribution on the Moon following the method of Sugano and Heki (EPS 2004; GRL 2005). We confirmed that we could recover the gravity anomalies similar to the Level-2 data with spatial resolution of ~0.8 degrees using low altitude portions of the data. Next, we downloaded the GRAIL Level-2 data set (spherical harmonics with degree/order complete to 660) together with the topography data by LRO laser altimetry, and tried to estimate the pin-point surface crustal density. First, we selected a certain square as large as ~60 km, and compared the gravity and topography values at grid points within the square. They are roughly proportional, and the slope provides information on the density of the material making the topography. This method, however, causes apparent positive correlation between density and average topographic height of about 0.2 g/cm^3/km. We (wrongly) assume that the mass anomalies lie on the reference surface. Then, the mass above (below) the reference surface is interpreted heavier/lighter than its real density. We performed a-posteriori correction of the altitude-dependent errors in the estimated density. We finally focus on a few positive gravity anomalies on the nearside (such as those close to the Copernicus crater) that are not associated with any topographic high. We will try to constrain the subsurface structure of the dense material responsible for the anomaly using both Level-1b and -2 data.

  10. Gravity is the Key Experiment to Address the Habitability of the Ocean in Jupiter's Moon Europa

    NASA Astrophysics Data System (ADS)

    Sessa, A. M.; Dombard, A. J.

    2013-12-01

    Life requires three constituents: a liquid solvent (i.e., water), a chemical system that can form large molecules to record genetic information (e.g., carbon based) as well as chemical nutrients (e.g., nitrogen, phosphorous), and a chemical disequilibrium system that can provide metabolic energy. While it is believed that there is a saline water layer located between the rock and ice layers in Jupiter's moon Europa, which would satisfy the first requirement, it is unknown if the other conditions are currently met. The likelihood that Europa is a haven for life in our Solar System skyrockets, however, if there is currently active volcanism at the rock-water interface, much the same that volcanic processes enable the chemosynthetic life that forms the basis of deep sea-vent communities at the bottom of Earth's oceans. Exploring the volcanic activity on this interface is challenging, as direct observation via a submersible or high-resolution indirect observations via a dense global seismic network on the surface is at present technically (and fiscally!) untenable. Thus, gravity studies are the best way to explore currently the structure of this all-important interface. Though mostly a silicate body with only a relatively thin (~100 km) layer of water, Europa is different from the terrestrial planets in that this rock-water interface, and not the surface, represents the largest density contrast across the moon's near-surface layers, and thus topography on this interface could conceivably dominate the gravity. Here, we calculate the potential anomalies that arise from topography on the surface, the water-ice interface (at 20 km depth), and the rock-water interface, finding that the latter dominates the free-air gravity at the longest wavelengths (spherical harmonic degrees < 10) and the Bouguer gravity at intermediate wavelengths (degrees ~10-50), and only for the shortest wavelengths (degrees > 50) does the water-ice interface (and presumably mass-density anomalies